Star Water Filter®
Targeted update: 3 November 2026

COMPARE TO MAKE AN INFORMED CHOICE

Gravity water filter comparison

Twelve configurations compared on their published analyses, tested volumes, certifications and flow rates.

A gravity water filter passes water through filter cartridges using gravity, without electricity or a connection to the water supply.

Based on the documentation criteria used, Star Water Filter® has the most comprehensive documentation in this comparison. Explore the evidence and differences that can help you choose.

NSF®-certified filter Exact scope documented
Independent laboratory analyses Published results
Documented stability Long-term reading
REACH compliance Material transparency

Why choose Star Water Filter®?

Filter tap water every day, with performance documented as litres accumulate.

Star Water Filter® systems work without electricity or a mains connection and use Ultimate Star Filter® cartridges.

01

Verifiable results. Published independent analyses up to 3,200 L per cartridge for the relevant chemical tests, beyond the nominal capacity of 3,000 L per cartridge. Relevant microbiological tests up to 3,000 L.

02

Practical flow rate. A new pair filters between 14 and 16 L/h, depending on operating conditions.

Prepare water for everyday drinks and cooking with a standalone system that needs no electricity or connection to the water supply.

03

Accessible evidence. The reports let you check the substances tested, measured reductions and volumes analysed.

Looking for a complete system for your home or cartridges for your compatible gravity equipment?

View analysis results

This comparison distinguishes claimed characteristics, test results and certifications to compare gravity filters on a verifiable basis. If you are still deciding between gravity, a filter jug, a tap filter, an under-sink filter or reverse osmosis, see our guide to the main solutions.

Compare water filtration solutions

How to read the evidence in this comparison

This comparison covers twelve gravity systems or configurations. The documents below answer different questions: their value depends on scope, protocol and checks performed, with no automatic ranking between a report and a certification.

Independent test report

Results for the substances tested, under the conditions and at the volumes stated.

Certification

Compliance with specific requirements for the listed product or component: materials or performance, depending on its scope.

Manufacturer information

Claimed characteristics and performance, distinct from results verified by a third party.

For each result, check the substance, tested volume and configuration: cartridge, pair or system. An initial test does not demonstrate maintained performance up to claimed capacity. No identified public evidence does not mean ineffectiveness. Flow rates are published values for the stated configurations, not results from a shared comparative test.

COMPARISON TABLE

Compare gravity water filters using evidence and the actual volumes published

This table compares information publicly available as of 3 November 2026. When the tested volume is known, it is shown in litres so that the claimed service life can be compared with what was actually measured. Evidence at 5 L, 100 L, 1,500 L or 3,000 L does not provide the same information about how a filter performs over time. Flow rates are the values published by manufacturers for the stated configurations; they may vary with water level, water quality, clogging and the number of cartridges. The absence of identified public evidence does not mean that a product is ineffective: it means that we did not find sufficiently clear public data on the point concerned.

Technical reading
Present

Technical characteristic identified in the system.

Not present

Characteristic not identified in the system as of the review date.

Claimed / partial

Characteristic claimed or documented with limited scope.

Level of proof
Published proof

Accessible and verifiable data; the tested volume is stated when known.

Partial proof

Real data, but limited by the volume, protocol, contaminant or model concerned.

No accessible proof

No sufficiently clear public data identified as of the review date.

On mobile, scroll the table horizontally to compare all systems.

To make reading easier, the table is divided into three blocks. Each block keeps the brands in columns and has its own horizontal scrollbar.

1. Filter architecture and design

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Targeted update on 3 November 2026: PGF9-2 added, CF163W NSF listing, Classic claimed capacity and Ultra Sterasyl PFOA/PFOS report. Other data are retained from the previous version; this update is not a new exhaustive verification of all products.

Berkey transition: depending on distributor stock and offers, systems may contain Black Berkey BB9 or Phoenix Gravity New Millennium Edition PGF9-2 elements. Check the elements included: characteristics, reports and certifications depend on the configuration. Phoenix KokoCarb remains a separate reference in this comparison.

Compared criterion Star Water Filter® Berkey / Black Berkey® Berkey · PGF9-2 Coldstream FTO+ British Berkefeld / Ultra Sterasyl Weeplow O’Pure 2 Euroguard Classic Phoenix KokoCarb Purewell K Series Katadyn Gravidyn Ecofiltro Orinko
Dominant filter architecture Multi-layer compositeActivated carbons, dedicated heavy-metals media, nanofiltration membrane and colloidal silver Proprietary composite mediaMedia blend claimed; detailed composition not published Activated-carbon blockCTC-60 coconut-shell carbon; moulded and sintered media according to NMCL. Ceramic + activated carbonCeramic shell + granular activated carbon Ceramic + activated carbonSterasyl® microfilter + granular activated carbon + lead-reduction media Activated carbon + 0.02 µm UFHollow-fibre ultrafiltration membrane; no nanofiltration Activated-carbon blockEuroguard Classic: compressed activated-carbon block Activated carbon + silverSilver-impregnated coconut-shell activated-carbon block Activated carbon + 0.01 µm UFK8012: activated carbon, silver ions and hollow-fibre UF membrane Silver-treated ceramic + activated carbonGravidyn cartridge for the Drip system Ceramic + activated carbon + silverClay/ceramic, activated carbon and colloidal silver Mainly activated carbonCoconut-shell activated carbon; little detail on any additional architecture
Detailed architecture beyond the main material Publicly documentedMulti-layer architecture explained and cross-referenced with published analyses Partially documentedProprietary media: mechanisms and full composition only partly detailed Partly documentedProcess described by NMCL; complete formulation not published. DocumentedCeramic and carbon clearly identified; relatively simple architecture DocumentedCeramic, carbon and lead-reduction media published; performance must be read criterion by criterion DocumentedCarbon + UF clearly claimed; finer composition less detailed Simple architectureThe Classic is clearly described as a compressed activated-carbon block Partially documentedCoconut carbon + silver published; little detail on the internal architecture beyond that Published architectureK8012 three-stage configuration clearly described by Purewell Published compositionSilver-treated microporous ceramic + high-performance activated carbon Published compositionThree materials clearly stated Limited detailActivated carbon stated, with little detail on any additional architecture
NSF®-certified activated carbons as filter media Documented internallySupplier certificates verified and held by SWF; not published to protect the formulation and suppliers Not identifiedNo public certificate for the activated carbon itself identified No evidence identifiedThe cartridge listing is not a certificate for the raw carbon as a medium. Not identifiedActivated carbon disclosed; NSF® certificate for the media not identified Not identifiedProduct/cartridge certifications are covered separately below Not identifiedTests according to certain standards must be distinguished from certification of the carbon itself No accessible proofA carbon block is listed under NSF® 42; this does not document the raw carbon itself as a certified filter media No accessible proofThe PCC8/KokoCarb cartridge is NSF® listed; this is not a certificate for the raw carbon itself No accessible proofNSF® documents are available for certain products/components; no public certificate identified for K8012 carbon as filter media Not identifiedActivated carbon disclosed; NSF® certificate for the media not identified Not identifiedActivated carbon disclosed; NSF® certificate for the media not identified Not identifiedActivated carbon disclosed; NSF® certificate for the media not identified
Nanofiltration membrane PresentIntegrated nanofiltration membrane Not present Not identified Not present Not present Not present0.02 µm ultrafiltration, not nanofiltration Not present Not present Not present0.01 µm ultrafiltration, not nanofiltration Not present Not present Not present
Bacteriostatic silver treatment PresentIntegrated colloidal silver Not publicly documented Not documentedNo silver treatment documented in the NMCL documents reviewed. PresentSilver incorporated into the ceramic according to the filter documentation PresentSilver used in the ceramic formulation Not documented Not documentedThe term “ionised carbon” is not sufficient to establish the presence of silver PresentSilver-impregnated KokoCarb cartridge PresentSilver ions stated in the K8012 composition PresentSilver incorporated into the ceramic PresentColloidal silver Not documented
Published filtration flow rate / compared configuration 14 to 16 L/hWith 2 new Ultimate Star Filter® elements; around 4 L/h at about 3,000 L. Flow-rate evolution is published over use. Up to 13.3 L/hBig Berkey® 8.5 L with 2 Black Berkey® elements, upper chamber full; flow rate decreases as the water level falls. Up to 15.9 L/hTwo elements, upper chamber full; NMCL-claimed value, decreasing with water level. 1 L/h per filterPublished minimum flow rate for one CF163W; no extrapolation to a pair Up to 1.7 L/hBritish Berkefeld 8.5 L system with 2 Ultra Sterasyl® cartridges; published manufacturer value 3.8 L/hWith 2 O’Pure 2 elements, value published by Weeplow. No public numerical valueNo clear numerical value identified for 2 Euroguard Classic cartridges on the public pages reviewed. Up to 16 L/hWith 2 KokoCarb cartridges, advertised commercial flow rate. Up to 15.1 L/hK Series K8626 with 2 K8012 filters: up to 4 gal/h claimed 4 L/hPublished value for the Gravidyn cartridge; not extrapolated to a pair. 1 to 2 L/hEcofiltro 20 L, single-piece ceramic system. 8 L/hWith 2 cartridges; 4 L/h claimed per cartridge.
Claimed service life / actual tested volume 6,000 L / pair3,000 L per filter; chemistry tested up to 3,200 L per filter, microbiology up to 3,000 L per filter 3,000 gal / element≈ 11,356 L claimed; tests published by contaminant, without demonstration up to that volume ≈ 20,820 L per pair claimedNMCL: 5,500 US gallons per pair; PFOA/PFOS monitored up to 1,500 L, NSF 42 chlorine/taste/odour at 4,000 L. 1,500 L / filter or 6 monthsMany contaminants are tested up to 3,000 L per CF163W filter, beyond the nominal capacity 6 monthsPFOA/PFOS monitored up to 3,000 L in the Ultra Sterasyl report; volumes unspecified for some other tests. No extrapolation per cartridge or pair. 22,000 L per pairBacteria tested up to 300 L; PFAS, viruses, pesticides and metals mainly tested at start-up 22,700 L per pair / 2–3 years claimedManufacturer-claimed capacity; chlorine tested up to 300 L, metals up to 50 L, detailed PFAS results up to 35 L. 20,000 L per pair / 12 monthsPFAS tested up to 1,500 L; chlorine/taste/odour NSF® certified up to 4,000 L 6,000 gal per pair ≈ 22,700 LCurrent K8012 capacity; public reports identified over 3 to 5 L and on an older K8627 system, not the current K8626 6 monthsNo nominal capacity in litres published; microbiological tests are cited without a stated filtered volume on the public datasheet 2 yearsNo clearly published nominal volume; PFAS tested on 1 L and other tests are mainly one-off 11,350 L / cartridgeMicroplastics tested on 1 L; PFAS test volume not publicly stated; no evidence up to 11,350 L

2. Stability, protocols and certifications

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Compared criterion Star Water Filter® Berkey / Black Berkey® Berkey · PGF9-2 Coldstream FTO+ British Berkefeld / Ultra Sterasyl Weeplow O’Pure 2 Euroguard Classic Phoenix KokoCarb Purewell K Series Katadyn Gravidyn Ecofiltro Orinko
Documented long-term stability / end-of-life Published proofChemistry up to 3,200 L per filter; microbiology up to 3,000 L per filter, for a nominal service life of 3,000 L per filter Partial proofBroad test file, but the identified tests do not track performance up to the ≈ 11,356 L claimed per element Partial proofPFOA/PFOS: 1,500 L; chlorine/taste/odour: 4,000 L. No overall monitoring demonstrated up to claimed capacity. Published proofMany criteria measured up to 3,000 L per CF163W filter; some performance figures decline significantly with volume Partial proofPFOA/PFOS monitored up to 3,000 L in the Ultra Sterasyl report; volumes unspecified for some other tests. No extrapolation per cartridge or pair. Very partialBacteria up to 300 L; other families mainly tested at start-up versus 22,000 L claimed per pair Partial proofPublished test volumes (35, 50 or 300 L depending on the contaminant) do not demonstrate maintained performance up to the claimed 22,700 L per pair. Partial proofPFAS up to 1,500 L and NSF® chlorine up to 4,000 L versus 20,000 L claimed per pair Not demonstrated≈ 22,700 L claimed per pair; public reports identified over 3 to 5 L and on an older K8627 system Not publicly quantifiableMicrobiological tests cited, but filtered volume not stated; replacement recommended after 6 months Not demonstrated over timeClaimed service life of 2 years; recent tests but mainly one-off Not demonstrated up to 11,350 LRecent analyses published, but no public follow-up up to the claimed capacity
Published independent analyses with readable protocol and volumes Published proofIndependent reports, readable protocols and volumes; several measurement points up to 3,000 / 3,200 L per filter Published evidence, but scatteredSeveral independent reports exist; some volumes are low or do not track performance up to the claimed service life Partial proofPublic reports; PFOA/PFOS monitored at several sampling points. RAYNU multi-contaminant report covers an initial test. Published proofDetailed datasheet, laboratory and volumes clearly published up to 3,000 L per CF163W filter Published proofPFOA/PFOS monitored up to 3,000 L in the Ultra Sterasyl report; volumes unspecified for some other tests. No extrapolation per cartridge or pair. Partial proofReports accessible; 300 L for bacteria, several other tests at start-up Partial proofIAPMO reports accessible, but tests target volumes far below the claimed service life Partial proofReports accessible, with volumes varying by contaminant Partial proofThird-party reports available, but dated 2020 and relating to a K8627 system; correspondence with the current K8626 is not established Partial proofIndependent laboratories cited by Katadyn; full reports and volumes not published on the datasheet reviewed Published evidence, but one-offSeveral recent reports accessible; little litre-by-litre follow-up over use Published evidence, but one-offPublished French laboratory analyses; volumes of some tests not stated
Analyses according to standards / accredited laboratory Published proofISO/IEC 17025 laboratories; NSF®/ANSI protocols or other methods identified by contaminant Partial proofSeveral independent laboratories and normative references, but an older and heterogeneous test file Partial proofNSF/ANSI, APHA, AOAC and EPA references depending on the report; testing distinct from certification. Published proofIAPMO R&T; NSF/ANSI 42, 53 and P231; ISO 17025-compliant laboratory Published normative evidenceNSF®/ANSI 42, 53 and 401 for specific performance claims; NSF/ANSI/CAN 372 for lead content Partial proofSGS / other laboratories; some tests reference NSF®/ANSI or EPA, others use internal methods Partial proofIAPMO; tests according to NSF®/ANSI 42/53 on certain criteria, at low volumes Partial proofLaboratories and NSF®, EPA, APHA or AOAC methods depending on contaminant Partial proofPublic laboratory reports, but old and not clearly linked to the current K8626 / K8012 Partial proofBachema cited as an independent laboratory; methods and volumes not detailed on the public datasheet Partial proofMeasurlabs ISO/IEC 17025 for certain tests; other laboratories depending on contaminant family Partial proofIndependent French laboratories, including analyses stated as performed under COFRAC accreditation according to published documents
Heavy-metals analyses under NSF® 53 conditions (pH 6.5 / 8.5) Published proofSeveral metals tested at pH 6.5 and 8.5, with measurements up to 3,200 L per filter Published proofMetal tests exist at pH 6.5 and 8.5; no public follow-up up to 3,000 gal Partial proofMetals reports published; monitoring at both pH values and up to nominal capacity not established in the documents reviewed. Partial proofMetals tested according to NSF®/ANSI 53 up to 3,000 L per CF163W filter; no dual pH 6.5 / 8.5 reading identified Partial proofLead published at pH 6.5; no dual pH 6.5 / 8.5 reading for Ultra Sterasyl Partial proofThirteen metals tested at start-up; some NSF®/ANSI 53 references Partial proofLead, cadmium and mercury tested up to 50 L, at approximately pH 6.5 only Partial proofMetals published, but pH conditions not equivalent to a full 6.5 / 8.5 reading Partial proofLead and mercury tested over about 3 L in a 2020 K8627 report; no NSF® 53 protocol at both pH values identified No comparable evidence identifiedNo public heavy-metals file under pH 6.5 / 8.5 conditions Partial proofMetals tested, without a public protocol equivalent to NSF® 53 at both pH values Partial proofPublished metal analyses, but no public protocol equivalent at both pH values
NSF® / ANSI certification: exact nature of the certification NSF®-listed filterUltimate Star Filter® USF-SWF-001: NSF/ANSI 42, material requirements only; lead-content requirements also assessed Black Berkey® not NSF® listedThe Berkey systems currently NSF® listed use Phoenix elements, which are different from the Black Berkey® elements compared here Published evidencePGF9-2 listed under NSF/ANSI 42: chlorine, taste and odour, tested at 4,000 L. Big/Royal/Travel with PGF9-2 also listed; no PFAS certification in this listing. NSF®-listed cartridgeCF163W: NSF/ANSI 42, material requirements only. No contaminant-reduction performance certified in this listing. Published proofUltra Sterasyl: NSF/ANSI 42 particulates, NSF/ANSI 53 cysts/turbidity, NSF/ANSI 401 microplastics, NSF/ANSI/CAN 372 lead content No product certification identifiedTests according to certain standards must be distinguished from NSF® certification NSF®-listed componentEuroGuard carbon block: NSF/ANSI 42, material and structural-integrity requirements only Published proofPCC8/KokoCarb: NSF/ANSI 42 chlorine / taste / odour up to 4,000 L; Phoenix systems also listed NSF® documents availableNSF/ANSI 42 and 372 on certain products/components; exact scope must be tied to the specific model and component concerned No NSF® certification identifiedFor the Gravidyn cartridge compared No NSF® certification identifiedLaboratory reports are published, but no NSF® listing identified Published proofOrinko cartridges: NSF/ANSI 42 for material safety only; NSF/ANSI/CAN 372 for lead content
Published material compliance (REACH, RoHS, NSF 372 or equivalent) Published proofREACH published: European compliance regarding chemical substances in materials; USF-SWF-001 filter NSF® listed for material requirements Not identified for Black Berkey®Current 372 listings concern systems fitted with Phoenix filters Published evidenceNSF 42 material requirements for the cartridge; NSF/ANSI/CAN 372 for Big, Royal and Travel with PGF9-2: lead content, not lead reduction in water. NSF®-listed cartridgeCF163W: NSF/ANSI 42, material requirements only. No contaminant-reduction performance certified in this listing. Published proofNSF/ANSI/CAN 372 on listed Ultra Sterasyl systems/cartridges No public evidence identified Partially documentedNSF/ANSI 42 for the carbon block on materials/integrity; NSF 372 claimed by the manufacturer Published proofNSF® material requirements and lead content documented in Phoenix listings Documents availableNSF/ANSI/CAN 372 assessments and material documents published for certain components/systems; exact coverage of the K8626 must be checked No public evidence identified No public evidence identified Published proofNSF/ANSI 42 material safety + NSF/ANSI/CAN 372 lead content

3. Analysed contaminants and overall reading

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Compared criterion Star Water Filter® Berkey / Black Berkey® Berkey · PGF9-2 Coldstream FTO+ British Berkefeld / Ultra Sterasyl Weeplow O’Pure 2 Euroguard Classic Phoenix KokoCarb Purewell K Series Katadyn Gravidyn Ecofiltro Orinko
Published PFAS analyses Published proofPFOA, PFOS and PFHxA monitored up to 3,200 L per filter Partial proofPFOA directly tested over 25 gal, about 95 L; the other compounds presented in the report rely on a surrogate approach Partial proofPFOA/PFOS report: sampling at 0, 250, 500, 1,000 and 1,500 L. Cartridge/pair configuration unspecified; no extrapolation to other PFAS. No evidence identifiedPFAS/PFOA/PFOS not identified in the CF163W datasheet reviewed Published evidencePFOA/PFOS: measurements up to 3,000 L in QFT report 22-131-PFOAS; calculated combined reduction of approximately 95.3% at the final sampling point. Configuration and exact commercial reference require clarification. Partial proofSeven PFAS tested at start-up only; no follow-up in litres Partial proofIAPMO report on seven PFAS; detailed tables up to 35 L, while the report states a 100 L test Partial proofPFOA and PFOS monitored up to 1,500 L No evidence identifiedThe standard K8012 compared here is not presented as a PFAS filter; no public PFAS report linked to this configuration was identified No evidence identified Partial proofIndependent report on three filters; one-off test on 1 L with heterogeneous results depending on the unit tested Published proofTwenty PFAS analysed by an independent laboratory; filtered test volume not publicly stated
Published TFA analyses Published proofTFA monitored up to 3,200 L per filter No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified No evidence identified
Published bacteria analyses Published proofBacteria monitored up to 3,000 L per filter Published evidence, but one-offMicrobiological challenge over 4 L after filter conditioning; no follow-up up to the ≈ 11,356 L claimed No evidence identifiedNo PGF9-2-specific report identified in the documents reviewed; do not transfer KokoCarb results. Published proofKlebsiella terrigena tested up to 3,000 L per CF163W filter Published proofE. coli / Typhoid / Klebsiella: >99.99% published; cumulative volume not stated Partial proofBacteria monitored up to about 300 L No dedicated Classic test identifiedThe Klebsiella test published by Euroguard concerns the carbon + UF Combi filter, not the Classic compared here Partial proofKlebsiella tested up to around 757 L Partial proofE. coli report over 5 L, dated 2020 and relating to a K8627 system, not the current K8626 Partial proofBachema tests on several bacteria cited by Katadyn; filtered volume not publicly stated Published evidence, but one-offE. coli and coliforms tested; no public follow-up over the claimed 2-year service life Published evidence, but one-offE. coli, coliforms and enterococci published; filtered test volume not stated
Published virus / viral marker analyses Published proofViruses monitored up to 3,000 L per filter Published evidence, but one-offMS2 and fr coliphages tested in a 4 L challenge; no follow-up up to the claimed service life No evidence identifiedNo PGF9-2-specific viral report identified in the documents reviewed. Published proofRotavirus tested up to 3,000 L per CF163W filter Not claimedDoulton explicitly states that British Berkefeld elements do not filter viruses Partial proofMS2 bacteriophage tested at start-up only No evidence identified for the Classic Partial proofRotavirus tested up to about 757 L No evidence identifiedNo viral report clearly linked to the K8626 / K8012 identified No evidence identified No evidence identified No evidence identified
Overall reading of the level of proof Monitored up to 3,000 / 3,200 L per filterBroad contaminant spectrum; nominal service life of 6,000 L per pair (3,000 L per filter) Broad test file, often limited volumesNumerous independent reports, but a major gap between several tested volumes and the 3,000 gal claimed per element Partial proofChlorine/taste/odour certification and published chemical tests; depth varies by contaminant, without overall validation of the claimed ≈ 20,820 L. Numerous tests at 3,000 L per filterSubstantial public documentation; performance varies by contaminant and no PFAS/TFA identified Good documentation, but volumes often not statedPFOA/PFOS monitored up to 3,000 L in the Ultra Sterasyl report; volumes unspecified for some other tests. No extrapolation per cartridge or pair. Real tests, often at start-upBacteria up to 300 L; many other families tested only on a new filter Partial proofPublished test volumes (35, 50 or 300 L depending on the contaminant) do not demonstrate maintained performance up to the claimed 22,700 L per pair. Real tests at intermediate volumesPFAS 1,500 L, NSF® chlorine 4,000 L; no consistent follow-up up to the 20,000 L claimed per pair Claimed capacity far above the tested volumes≈ 22,700 L claimed per pair; quantifiable public reports over 3 to 5 L and on an older K8627 Microbiology documented, volume not statedTechnically credible brand, but little public data on PFAS/TFA and on actual tested volumes Several recent tests, mostly one-offPFAS tested on 1 L; no public follow-up up to the 2-year service life Several recent tests, without follow-up to 11,350 LPFAS, bacteria and microplastics published; volumes often unstated or very low

The mentions “partial proof”, “claimed” or “no accessible proof” describe only the documentation identified. For Star Water Filter®, NSF® certificates for certain families of filter media are verified and held internally, but are not published so as not to disclose suppliers and the filter formulation; they are therefore not presented here as public evidence. The public NSF® certification of Ultimate Star Filter® USF-SWF-001 is shown with its exact scope. The most useful approach is to compare what is tested, over how many litres, under which protocol and how closely this approaches the claimed service life.

BRAND-BY-BRAND READING

What the table actually shows, brand by brand

For each brand, the review below first compares what is claimed, what has actually been tested and, when the information is available, over how many litres. This is often more meaningful than a certification logo or a percentage obtained on a new filter. Flow rate is also taken into account because a filter must remain practical in daily use. For a broader explanation, see also how to tell whether a water filter is truly effective.

Star Water Filter®

Most comprehensive documentation

Quick read

Designed in France, Ultimate Star Filter® has a claimed service life of 6,000 L per pair, i.e. 3,000 L per filter. Chemical analyses are published up to 3,200 L per filter and microbiology up to 3,000 L per filter, by independent ISO/IEC 17025-accredited laboratories. Readers can therefore directly compare the claimed service life with the volumes actually tested.

Key points

  • French design and documented multi-layer architecture.
  • Independent ISO/IEC 17025-accredited laboratories and full reports published.
  • Chemical analyses up to 3,200 L per filter, beyond the nominal service life of 3,000 L per filter.
  • Microbiology up to 3,000 L per filter: bacteria, Salmonella and viruses.
  • Broad spectrum analysed through end of service life: PFAS and TFA, heavy metals, pharmaceutical residues, plastic derivatives, hormones, pesticides, VOCs, halogenated VOCs and microplastics.
  • One of the highest flow rates in the comparison: 14 to 16 L/h with a new pair, then around 4 L/h at about 3,000 L.
  • Ultimate Star Filter® NSF® listed; supplier certifications for certain media are verified and held by SWF.
  • Published REACH compliance: European compliance regarding chemical substances present in materials.

Good to know

Flow rate naturally decreases with use: it typically moves from 14–16 L/h with a new pair to around 4 L/h at about 3,000 L. This evolution is published, so users know what to expect over the filter’s service life.

Why SWF stands out

Ultimate Star Filter® combines several advantages that are rarely found together: French design, independent analyses up to 3,000–3,200 L per filter across a broad and coherent range of pollutants, fast yet controlled flow rate, NSF® certification and REACH compliance. With a nominal service life of 6,000 L per pair (3,000 L per filter), the main advantage is simple: performance is documented through the filter’s service life, and even beyond it for most chemical analyses.

Berkey / Black Berkey®

Quick read

Berkey has built strong recognition over many years. However, a pair of Black Berkey® elements is claimed to last about 22,700 L, while the public tests identified cover much lower volumes depending on the contaminant. The available results therefore do not demonstrate that the same performance is maintained through the claimed service life.

What the data show

  • Around 22,700 L claimed for a pair of Black Berkey® elements.
  • Flow rate up to 13.3 L/h on the 8.5 L Big Berkey® with two elements and a full upper chamber.
  • PFOA directly tested up to about 95 L in the report identified.
  • Microbiological challenge identified over about 4 L of contaminated water after filter conditioning.
  • Several of the technical reference reports identified are old, particularly those concerning metals and PFAS.

What to put in perspective

A good result over 4 L, 95 L or a few hundred litres does not show that the same performance will still be present after more than 22,000 L for the pair. Black Berkey® is not the filter used in the Berkey systems currently NSF® listed with Phoenix elements: that is a different configuration.

Overall reading

The key point with Black Berkey® is the gap between a very high claimed capacity and the volumes actually covered by public analyses. The brand’s long-standing reputation does not replace verification of performance after several thousand litres.

Berkey / Phoenix New Millennium PGF9-2

CTC-60 coconut-shell carbon; moulded and sintered media according to NMCL.

  • NMCL: 5,500 US gallons per pair; PFOA/PFOS monitored up to 1,500 L, NSF 42 chlorine/taste/odour at 4,000 L.
  • PGF9-2 listed under NSF/ANSI 42: chlorine, taste and odour, tested at 4,000 L. Big/Royal/Travel with PGF9-2 also listed; no PFAS certification in this listing.
  • PFOA/PFOS report: sampling at 0, 250, 500, 1,000 and 1,500 L. Cartridge/pair configuration unspecified; no extrapolation to other PFAS.

Chlorine/taste/odour certification and published chemical tests; depth varies by contaminant, without overall validation of the claimed ≈ 20,820 L.

Coldstream FTO Plus (CF163W)

Quick read

Coldstream publishes results for a substantial number of contaminants, including several measurements carried out up to 3,000 L per CF163W filter. The published nominal capacity is 1,500 L per filter. However, no PFAS or TFA analyses were identified in the datasheet reviewed, and some performance figures decline significantly with volume.

What the data show

  • IAPMO R&T tests according to NSF/ANSI 42, 53 and P231; laboratory compliant with ISO 17025.
  • Klebsiella, Rotavirus, numerous metals, VOCs, pesticides, pharmaceutical residues and hormones measured up to 3,000 L per CF163W filter.
  • Claimed nominal capacity: 1,500 L.
  • Published minimum flow rate: 1 L/h per CF163W filter.

What to put in perspective

  • At 3,000 L per filter, some reductions fall sharply: free chlorine is published at 80.5% and fluoride at 17.05%.
  • No PFAS or TFA analysis identified in the CF163W datasheet reviewed.
  • CF163W: NSF/ANSI 42, material requirements only. No contaminant-reduction performance certified in this listing.

Overall reading

Coldstream documents several performance figures up to 3,000 L per CF163W filter, beyond its nominal capacity of 1,500 L per filter. Contaminants must nevertheless be considered one by one: some performance figures remain high, while others fall sharply. The published minimum flow rate is also 1 L/h per filter.

British Berkefeld / Ultra Sterasyl

Quick read

Ultra Sterasyl has a PFOA/PFOS report with measurements up to 3,000 L. The exact configuration requires clarification; not all other test volumes are documented. The two-cartridge system flow rate is stated in the table.

What the data show

  • Sterasyl® ceramic + granular activated carbon + lead-reduction media.
  • Published NSF/ANSI certifications on several criteria, including particulates, cysts/turbidity and microplastics depending on the model.
  • Bacteria, Cryptosporidium and Giardia: published performance above 99.99% in Doulton tables.
  • PFOA/PFOS: measurements up to 3,000 L in QFT report 22-131-PFOAS; calculated combined reduction of approximately 95.3% at the final sampling point. Configuration and exact commercial reference require clarification.
  • Typical flow rate: 1 L/h per Ultra Sterasyl, i.e. around 2 L/h with two cartridges.

What to put in perspective

  • Replacement recommended after 6 months, with no nominal capacity in litres published for Ultra Sterasyl.
  • The QFT report names Ultra Sterasyl but does not specify W9121226; the entries “Plumbed in” and “Gravity Candles fitted into SS Gravity Housing” leave the configuration to be clarified. This PFOA/PFOS monitoring does not extend to other contaminants.
  • Doulton states that British Berkefeld elements do not filter viruses.
  • The slow flow rate of the ceramic can become restrictive in daily use.

Overall reading

PFOA/PFOS monitored up to 3,000 L in the Ultra Sterasyl report; volumes unspecified for some other tests. No extrapolation per cartridge or pair.

Weeplow O’Pure 2

Quick read

The O’Pure 2 pair is claimed to last 22,000 L and a flow rate of 3.8 L/h. Bacteria are tested up to about 300 L, while PFAS, MS2 virus, pesticides and metals are mainly tested on a new filter or at start-up.

What the data show

  • Activated carbon + hollow-fibre ultrafiltration 0.02 µm.
  • Bacteria monitored up to about 300 L.
  • Seven PFAS analysed at filter start-up.
  • MS2 virus, pesticides and heavy metals tested on a new filter / at start-up according to the reports identified.

What to put in perspective

The difference between 22,000 L claimed and tests at 300 L or at start-up remains considerable. These reports show performance under the tested conditions, but not that it is maintained after several thousand litres.

Overall reading

The key point with Weeplow is not the number of reports displayed, but the gap between the claimed service life and the actual tested volume for each contaminant family.

Euroguard Classic

Quick read

22,700 L per pair / 2–3 years claimed. Manufacturer-claimed capacity; chlorine tested up to 300 L, metals up to 50 L, detailed PFAS results up to 35 L.

What the data show

  • Chlorine tested up to 300 L.
  • Lead, cadmium and mercury tested up to 50 L.
  • Seven PFAS analysed; visible result tables up to 35 L in the report reviewed.
  • No clear numerical flow rate identified for the two-cartridge Classic configuration on the public pages reviewed.

What to put in perspective

  • The published Klebsiella bacterial test concerns the carbon + UF Combi filter, not the Classic compared here.
  • The NSF® listing identified covers material / structural-integrity requirements; it does not prove PFAS reduction over 11,356 L.
  • The PFAS report states 100 L in its summary, while the visible result tables go up to 35 L.

Overall reading

Published test volumes (35, 50 or 300 L depending on the contaminant) do not demonstrate maintained performance up to the claimed 22,700 L per pair.

Phoenix KokoCarb

Quick read

Phoenix claims 20,000 L for a pair of KokoCarb cartridges and a flow rate of up to 16 L/h. However, the actual published volumes vary widely by contaminant: about 757 L for microbiology, 1,500 L for PFOA/PFOS and 4,000 L for chlorine.

What the data show

  • Silver-impregnated coconut-shell activated-carbon block.
  • PFOA/PFOS up to 1,500 L in the report identified.
  • NSF/ANSI 42: chlorine / taste / odour reduction up to 4,000 L for PCC8/KokoCarb.
  • Klebsiella and Rotavirus tested up to about 757 L in the reports identified.
  • Claimed flow rate: up to 16 L/h with two cartridges.

What to put in perspective

The issue is not the absence of tests, but their varying depth: 757 L, 1,500 L or 4,000 L depending on the contaminant, for a pair claimed to last 20,000 L. Phoenix also recommends replacing the cartridges every 12 months. No TFA analysis was identified.

Overall reading

Phoenix combines a high flow rate with several published tests, but the data do not show that all performance remains unchanged up to the claimed 20,000 L.

Purewell K Series Classic (K8626 / K8012)

Quick read

The Purewell K Series Classic K8626 uses two K8012 filters and claims up to 6,000 gallons per pair, about 22,700 L, with a flow rate of up to about 15.1 L/h. However, the public performance reports identified are dated 2020, concern an older K8627 system and cover only 3 to 5 L for the quantifiable tests.

What the data show

  • K8012 architecture: activated carbon + silver ions + 0.01 µm UF membrane.
  • Current advertised capacity: up to 6,000 gallons per pair, about 22,700 L.
  • Claimed flow rate: up to 4 gal/h with two filters, i.e. about 15.1 L/h.
  • Purewell provides a public centre gathering certificates and performance reports.

What to put in perspective

  • Bacterial report identified: 5 L, on a 2020 K8627 system.
  • Chlorine / lead / mercury report identified: about 3 L, also on a 2020 K8627.
  • These reports do not concern the current K8626 system, although they relate to a previous-generation Purewell gravity system.
  • No identified public follow-up makes it possible to verify performance up to the roughly 22,700 L claimed for the pair.
  • No public PFAS report was identified for the standard K8012 filter compared here.

Overall reading

The current K Series advertises a high capacity and flow rate, but the comparison should focus above all on what has actually been tested: the quantifiable public reports found cover only a few litres and an older K8627 model, far from the currently claimed capacity.

Katadyn Gravidyn

Quick read

Katadyn Gravidyn combines silver-treated microporous ceramic and activated carbon, with replacement recommended no later than after 6 months. Katadyn cites independent microbiological tests, but the public documentation reviewed does not state how many litres had been filtered during these tests.

What the data show

  • Bachema tests cited on several bacteria, including E. coli and Salmonella.
  • Ceramic with incorporated silver + high-performance activated carbon.
  • Published Gravidyn flow rate: 4 L/h.
  • Replacement recommended after 6 months.

What to put in perspective

  • Microbiological test volume not stated in the public documentation identified: it is impossible to know whether performance was verified after hundreds or thousands of litres.
  • No public file identified on PFAS, TFA or viruses for Gravidyn.
  • The 4,000 L figure sometimes associated with Katadyn concerns another product and is not used for Gravidyn.

Overall reading

Katadyn publishes microbiological information, but without a public test volume these results cannot be turned into evidence of performance over time. This missing information limits comparison with filters tested over several thousand litres.

Ecofiltro

Quick read

Ecofiltro recommends replacing its filter unit after 2 years, with no clearly published nominal volume in litres. The 20 L model filters about 1 to 2 L/h. Several recent reports exist, but the tests identified remain one-off.

What the data show

  • Architecture: clay/ceramic + sawdust-derived activated carbon + colloidal silver.
  • Public reports on bacteria, PFAS, microplastics, pesticides, heavy metals and pharmaceutical residues.
  • Ecofiltro 20 L flow rate: 1 to 2 L/h.

What to put in perspective

  • The Measurlabs PFAS report covers 1 L per unit.
  • The three units tested give heterogeneous results for some PFAS.
  • No identified public follow-up links these one-off tests to the claimed service life of 2 years.
  • No public TFA or viral test identified.

Overall reading

Ecofiltro now has several reports, but the most important information for service life is still missing: up to how many litres have these performance figures been verified?

Orinko

Quick read

Orinko claims 11,350 L per cartridge, i.e. 22,700 L with two cartridges, and a flow rate of 8 L/h with two cartridges. Analyses are published, but the filtered volume is not stated for several important tests.

What the data show

  • 20 PFAS analysed; cumulative filtered volume not stated in the public information identified.
  • Microplastics tested by FILAB over 1 L.
  • Bacteria analysed with before/after results; cumulative volume not clearly stated publicly.
  • Claimed flow rate: 4 L/h per cartridge, i.e. 8 L/h with two.
  • NSF® certification must be read according to the exact scope of the official listing, separately from contaminant-performance reports.

What to put in perspective

A before/after analysis without a stated cumulative volume shows what happens under the test conditions, but not after several thousand litres. For microplastics, the volume is known: 1 L tested, compared with the 11,350 L claimed per cartridge.

Overall reading

With Orinko, the key point is therefore simple: 11,350 L claimed per cartridge, but several analyses do not state the tested volume, and the microplastics test was performed on 1 L. This does not document performance through the claimed service life.

SCIENTIFIC CRITERIA

The most useful criteria for seriously comparing a gravity water filter

Not all criteria carry the same weight in a comparison. Some provide surface information, while others allow a finer reading of the technical consistency, the quality of the evidence and real credibility of a system.

01

Filter architecture

The internal composition of a filter largely determines how it works. Activated carbons, ceramic, hollow fibres or a nanofiltration membrane do not serve the same purposes or the same families of contaminants. In gravity filtration, this architecture must also be read alongside the flow rate and the contact time between water and filter materials.

A system whose architecture is clearly documented is generally easier to compare than a system whose components remain vague or are merely mentioned.

02

An architecture backed by performance testing

Ultimate Star Filter® combines activated carbons, a dedicated heavy-metal medium and an integrated electroadsorptive membrane. The value of this architecture is assessed through published results: substances analysed, reductions measured and monitoring as litres accumulate.

The presence of a component alone does not demonstrate the effectiveness of the complete filter. Performance is assessed by considering design together with test results.

03

Long-term stability

An announced service life does not, by itself, provide sufficient information. The decisive point is whether performance remains readable across the litres filtered and up to volumes close to the recommended end-of-life.

The documented long-term stability is often the most useful criterion for distinguishing a commercial promise from performance that is actually monitored.

04

Level of proof and protocol

Manufacturer data, certification, regulatory compliance and independent analysis do not provide the same level of information. Comparing them without distinction often leads to hasty conclusions.

A serious comparison must rank the evidence and prioritise what can be verified, reread and placed within an identifiable protocol, such as laboratory analyses. This is especially true when test conditions strongly influence results, for example for certain heavy-metals tests.

05

Demanding contaminants and test conditions

Certain emerging or highly discussed contaminants, such as PFAS, the TFA or certain heavy metals, require more rigorous reading than standard tests. Their presence in a comparison can reveal a higher level of requirement in the published documentation.

It is still necessary to look at the volume at which these analyses are performed, and under which conditions. For heavy metals, tests conducted under conditions comparable to NSF® 53, especially at pH 6.5 and 8.5, provide a much stronger reading.

06

Material compliance, REACH and system consistency

The quality of a system depends not only on what it filters, but also on what it puts in contact with water. The material compliance, when clearly published, provides useful information on the manufacturer’s transparency.

This consistency can also be seen in the system’s complementary technical choices, for example the presence of a silver-based bacteriostatic treatment. This type of element does not replace filtration analyses, but it complements the reading of a system when architecture, materials and performance are documented together.

07

Filtration flow rate and ease of use

A filter may look effective on paper but become restrictive if users have to wait hours for a few litres of water. The flow rate is therefore a genuine practical criterion, provided comparable configurations are used and the figure is understood in context: full chamber, new filter or minimum value.

A fast flow rate does not, on its own, prove good filtration. The real value lies in combining practical flow rate with performance verified over time. With Ultimate Star Filter®, a new pair typically filters 14 to 16 L/h, with around 4 L/h still available at about 3,000 L of use, while performance is analysed up to 3,000–3,200 L per filter.

Taken in isolation, no single criterion is sufficient. The most useful reading is based on their overall consistency: architecture, level of proof, stability over time, depth of analyses and test conditions.

Which Star Water Filter® equipment should you choose?

Looking for a complete system to filter tap water?

Star Water Filter® systems work without electricity, drilling or a mains connection. They use the same Ultimate Star Filter® cartridges: choose your size according to household consumption, available space and preferred finish.

Choose my SWF system

Already own a compatible gravity system?

You can replace its filter elements with Ultimate Star Filter® cartridges without buying another complete system. Check the dimensions and compatibility requirements on the product page.

Check USF cartridge compatibility

Looking for documented reduction of a specific contaminant?

Check the results for the substance you are concerned about: PFOA, PFOS, TFA, lead or perchlorates, for example. Published reports specify test conditions, volumes analysed and measured reductions for the relevant parameters.

View USF analyses

KEY TAKEAWAY

What truly distinguishes gravity water filters

  • Readable architecture → clearly identified and consistent components
  • High level of proof → published independent analyses
  • Credible test conditions → protocols comparable to recognised standards (e.g. NSF® 53)
  • Depth of analyses → PFAS, TFA, heavy metals, bacteria, viruses
  • Long-term stability → results followed up to volumes close to end-of-life
  • Practical flow rate → sufficient filtration speed for daily use, without sacrificing evidence of performance

Essential reading

A high-performing filter is not recognised by a single indicator, but by the consistency between design, analyses, tested volume, flow rate and test conditions.

The most accomplished systems are those that make these elements readable, verifiable and consistent, including in particular the number of litres over which performance was actually tested.

To go deeper into your choice, see the complete buying guide or discover the criteria that distinguish the most accomplished systems.

TO GO FURTHER

Choose a documented filter, not just an announced filter

Among the 12 systems reviewed, Star Water Filter® presents the most comprehensive documentation according to the criteria selected. Ultimate Star Filter® combines French design, analyses carried out by accredited independent laboratories, a broad spectrum of pollutants tested up to 3,000 to 3,200 L per filter, a fast yet controlled flow rate, NSF® certification and REACH compliance. Its nominal service life is 6,000 L per pair, i.e. 3,000 L per filter: the analysis volumes are therefore directly comparable with the claimed service life.

Discover Star Water Filter® filters

SOURCES

Sources and documents reviewed

Targeted update of Berkey PGF9-2, Coldstream NSF, Euroguard Classic and Ultra Sterasyl PFOA/PFOS data. Other data are retained from the 20 August 2026 version and have not undergone a new exhaustive verification.

Manufacturers’ websites and documentation may change. The links below are the main sources used for the current version of this comparison.

For the flow rate, we use, wherever possible, a standard configuration with two filter elements, a very common setup among the gravity systems compared. When a manufacturer publishes only a value per cartridge or per system, we keep that figure as published and state it clearly. When no clear numerical value is published, we simply state “no public numerical value”.

Star Water Filter®

Berkey / Black Berkey®

Berkey / PGF9-2

Coldstream FTO Plus

British Berkefeld / Ultra Sterasyl

Weeplow O’Pure 2

Euroguard Classic

Phoenix KokoCarb

Purewell K Series

Katadyn Gravidyn

Ecofiltro

Orinko

SWF note: some NSF® certifications for media used in the Ultimate Star Filter® formulation are held internally and intentionally not published, because disclosure could identify suppliers and formulation components. They are therefore kept separate from the public documents listed above.

Analysis methodology

Methodology

Analysis based on public data, laboratory test protocols and a critical reading of long-term performance.

Author Star Water Filter® technical team

This content is written by the Star Water Filter® technical team, specialising in the analysis of gravity-filtration systems. It is based on public documents, independent laboratory reports, certification registers and a comparison of actual tested volumes, published flow rates and claimed service lives. When SWF information is documented internally but confidential, this distinction is explicitly stated.

FAQ

Frequently asked questions about the gravity water filter comparison

This FAQ complements the comparison by answering the most frequent questions about comparison criteria, proof reading and the choice of a gravity filtration.

What is the best gravity water filter?

There is no single best gravity water filter in absolute terms: the right choice depends in particular on intended use, budget, required capacity and the level of evidence expected. Among the 12 systems reviewed here, Star Water Filter® nevertheless presents the most comprehensive documentation according to the criteria selected: nominal service life of 6,000 L per pair (3,000 L per filter), published chemical analyses up to 3,200 L per filter, microbiology up to 3,000 L per filter, PFAS/TFA and detailed architecture. This conclusion relates to the level of documentation and evidence assessed, and does not constitute a universal ranking across every possible criterion.


How can gravity water filters be compared seriously?

A serious comparison is not just about comparing brands or marketing promises. Manufacturer data, certifications, regulatory compliance and independent analyses must be distinguished. The most useful criteria are generally the filter architecture, the documented long-term stability, the actual tested volume, the depth of published analyses and the filtration flow rate for daily use.

Why is the announced service life not sufficient?

An announced service life in litres or months remains declarative information if it is not accompanied by analyses performed at different stages, especially near the recommended end-of-life. The real issue is whether performance remains readable over time, and not only at the beginning of use.

Does NSF® certification always guarantee filtration performance?

No. An NSF® mention must always be read in detail, because it can cover different aspects depending on the case. Some certifications concern materials or sanitary safety, while others directly concern filtration. It is therefore important to check precisely what the certification covers. See also: NSF® certification and the Ultimate Star Filter® water filter.

Why is long-term stability a central criterion?

Because a new filter does not tell the whole story about how the system behaves after several hundred or thousand litres. Documented stability makes it possible to read whether performance remains consistent over use. It is often the most useful criterion for distinguishing an announced promise from actually monitored performance.

Why is filter architecture important?

Architecture largely determines the technical profile of the system. Activated carbons, ceramic, hollow fibres or a nanofiltration membrane do not play the same role. Understanding a filter’s architecture helps better interpret published analyses and check whether results are consistent with the components used.

Should PFAS and TFA be looked at in a comparison?

Yes, when the documentation includes them. The PFAS, the TFA and certain demanding contaminants often help distinguish the most rigorous systems in their analytical approach. But these results must always be read with their protocol, test volume and place within the overall proof system.

What should be remembered from this comparison when choosing a system?

The most important point is to compare consistent evidence rather than isolated promises. As of the date of writing, the most convincing systems are those that make their architecture readable, publish independent analyses, document long-term stability and provide a clear level of proof on the truly decisive criteria. For more practical guidance, you can also consult the buying guide.