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Environmental impact & alternatives
Publié le 02/11/2026
Bottled water or filtered water: how much could you really save?
COST • EVERYDAY USE • FILTERED WATER
Buying a bottle of water feels like a small expense. Repeated every week, it can add up to hundreds of euros. A gravity filtration system requires an upfront investment: at what point can it become the more economical option?
Short answer: for a €370 stainless-steel Big Star, bottled water assumed to cost €0.30/L and the French reference tap-water price, the system breaks even within two years if it replaces about 1.72 litres of bottled water per day. Actual savings depend on your prices and habits.
· Star Water Filter® editorial team
Key takeaways — Four essentials for a meaningful comparison
- Include the cost of the complete system and tap water, not only replacement cartridges.
- The included pair of filters has a combined nominal capacity of 6,000 L and a recommended service period of approximately two years.
- At 4 L/day and €0.30/L bottled water, our illustrative two-year saving with the stainless-steel Big Star is approximately €492.
- If bottled water is cheaper, or you drink little of it, the saving may be smaller or even negative over two years.
A COMMON MISTAKE
Comparing the price of a bottle with the price of a cartridge
A filtration system’s real cost cannot be reduced to the purchase price or to the maximum number of litres advertised. Compare expenses over the same period and the same actual consumption, including when cartridges need to be replaced.
Actual use
A household using 1 L/day will not spread the initial cost in the same way as one using 6 L/day.
Bottled-water price
Whether you pay €0.15 or €0.30 per litre makes a substantial difference.
Replacement interval
A capacity expressed in litres does not remove the need to follow the recommended replacement schedule.
TRANSPARENT ASSUMPTIONS
What figures are we using?
This is a French reference scenario, prepared in November 2026. It does not represent average prices in Ireland, the UK or other countries. The bottled-water price is a modelling assumption, not an official national average.
€370
Big Star stainless-steel complete system, with two filters included, reference retail price.
€150
Price of a replacement pair of Ultimate Star Filter® cartridges for the following period.
€4.89/m³
French national average water and wastewater price on 1 January 2025, around €0.00489/L.
€0.30/L
Assumed price of bottled water replaced in the main scenario.
The €4.89/m³ figure published by Eaufrance is based on a standard annual bill for 120 m³, including fixed charges. It is a reference average, not the exact marginal price paid by every household. Optional accessories, any delivery charges and routine maintenance are excluded. SWF prices may change.
THE COMPARISON THAT MATTERS
How much could you save over two years?
Examples over 730 days, using bottled water at €0.30/L, a €370 Big Star and tap water at €0.00489/L. All illustrated volumes remain below the combined nominal capacity of the two included filters.
Light use · 1 L/day
730 L over 2 years. · Bottled water : 219.00 €. · Big Star + tap water : 373.57 €. · Extra cost : 154.57 €.
Low consumption · 2 L/day
1,460 L over 2 years. · Bottled water : 438.00 €. · Big Star + tap water : 377.14 €. · Saving : 60.86 €.
Everyday use · 4 L/day
2,920 L over 2 years. · Bottled water : 876.00 €. · Big Star + tap water : 384.28 €. · Saving : 491.72 €.
Higher-use household · 6 L/day
4,380 L over 2 years. · Bottled water : 1,314.00 €. · Big Star + tap water : 391.42 €. · Saving : 922.58 €.
These are illustrative comparisons, not guaranteed savings. Each filtered litre is assumed to replace a litre you would otherwise have bought in a bottle.
A WORKED EXAMPLE
Four litres per day: the full calculation
Over two years, 4 L/day amounts to 2,920 L. At €0.30/L, bottled water costs €876. The stainless-steel Big Star costs €370, while the corresponding tap water costs €14.28 at the reference rate, giving a total of €384.28. The difference is €491.72 in favour of the filtration system.
In this example, the complete filtered-water cost over the first two years is approximately €0.132/L. Do not confuse this with €0.025/L, the theoretical cartridge-only cost (€150 ÷ 6,000 L) when their full nominal capacity is actually used.
BOTTLED-WATER PRICE MATTERS
What if your bottled water costs €0.15/L?
At 4 L/day, 2,920 litres then cost €438 in bottles, compared with €384.28 for filtered water in our example. The two-year saving falls to just €53.72. At a lower bottled-water price, the initial system cost might not be recovered within two years.
BREAK-EVEN POINT
How much bottled water must you replace?
Use this simple formula: system price ÷ (bottled-water price per litre − tap-water price per litre). With the main assumptions, the break-even volume is about 1,254 L, or 1.72 L/day over two years. At €0.15/L bottled water, it rises to about 2,550 L, or 3.49 L/day.
This break-even point only concerns direct spending during the initial two-year period. Optional costs and resale value are not included.
REAL USE, NOT A FIXED PROMISE
Why doesn’t nominal capacity guarantee a fixed cost per litre?
The supplied pair has a combined nominal capacity of 6,000 L (3,000 L per filter), with a recommended service period of approximately two years. Not every household will consume all 6,000 L before replacement is due.
You use little water
At 1 L/day, only 730 L are used over two years, so the initial purchase is spread over relatively few litres.
You use more
At 6 L/day, 4,380 L are consumed over two years, spreading the same upfront cost across more litres.
After two years
Allow for the recommended replacement pair, priced at the rate applicable when you buy it.
Outside France
Substitute local water tariffs, bottled-water prices and commercial conditions before using these figures.
BEYOND THE NUMBERS
What changes in everyday life?
The appeal of gravity filtration goes beyond comparing two prices per litre. A system that suits your household may also change everyday routines.
Fewer bottles to carry
Less buying, lifting and storing bottled water if you genuinely replace it with filtered tap water.
No plumbing or electricity
The system works by gravity, without connecting to the water mains or requiring electricity.
A size for your household
Mini Star, Big Star and Super Star are selected according to household size and habits.
Documented filtration
Ultimate Star Filter® test results are available in independent laboratory reports with the relevant testing conditions and volumes.
BEFORE YOU BUY
Four questions worth asking
How much bottled water do you really buy?
Count only bottles you would actually replace, not all water used in your home.
What do you pay per litre?
Check receipts or shopping records to replace our assumption with your actual price.
Which system suits you?
A larger tank does not automatically produce a greater saving.
How is filtration performance documented?
Running costs matter, but so do the evidence and reports behind the filter.
CONCLUSION
The best calculation is the one based on your household
For people who buy several litres of bottled water every day, gravity filtration may offer meaningful savings as well as everyday convenience. For occasional users or those buying very inexpensive bottled water, recovering the initial investment takes longer. Use your own figures rather than relying on a saving quoted without context.
One litre can look inexpensive. Two years of habits tell a different story.
FURTHER READING
Make an informed choice
Find the right capacity
View laboratory test results
Replacement cartridge prices
Explore Star Water Filter® systems
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Star Water Filter®
The technical content published on this website is written and validated by the Star Water Filter® technical team.
It is based on independent laboratory analyses, performance data from the Ultimate Star Filter® and experience gained in the design and use of gravity filtration systems.
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