What a filter really costs, over five years.
The price on the box is the down payment. This adds every cartridge you will buy, replaced at the maker’s gallon or month rating, whichever comes first.
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How the numbers work
- Prices are each maker’s own list price, never a retailer’s sale price. Each statement says when it was checked. Prices change; the maker’s page is the final word.
- Replacement timing uses the maker’s rating in gallons and in months, whichever runs out first for your household. The system ships with its first cartridges, so those are not counted twice.
- Water use starts at 1 gallon of drinking and cooking water per person per day. That is TapBuff’s assumption, not a measured figure; change it to match your home.
- Whole-house systems see every gallon the house uses, so they start at 80 gallons per person per day, also an assumption. For scale, EPA says the average American family uses more than 300 gallons a day at home.
- Not included: installation, plumbing parts, electricity for pumps or UV lamps, and the water an RO system sends to drain.