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The True Cost of a Water Filter, per Gallon

The cheapest filter to buy is often the most expensive water to drink. We calculated the real cost per gallon — price ÷ certified capacity — for 258 certified filters. Pitcher filters cost about 20× more per gallon than under-sink filters.

What this means, in plain English

Water filters have two prices: what you pay at the store, and what each gallon of filtered water actually costs over the life of the filter. The second one is what matters — and it often flips the first. A cheap pitcher looks like a bargain, but its filter only cleans a small number of gallons before you replace it, so the water works out expensive. An under-sink filter costs more up front but cleans thousands of gallons, so each gallon is far cheaper. We divided each filter’s price by the gallons it’s certified to handle to get its true cost per gallon.

What you can do

If you filter water every day, look past the sticker price and compare cost per gallon. An under-sink filter usually pays for itself quickly versus pitchers or fridge filters — and often filters more contaminants too.

Median cost per gallon, by filter type

The real price of the water, not the filter. Lower is cheaper per gallon.

Cheapest certified filters, by true cost per gallon

Shoppable, consumer filters ranked by cost per gallon. Search by brand or type.

No matches.

Terms, explained

Cost per gallon

The filter’s purchase price divided by the gallons it’s certified to treat before replacing. It’s the fairest way to compare filters of different sizes.

Certified capacity

How many gallons a filter is independently tested and certified to handle before its performance drops. Bigger capacity usually means cheaper water per gallon.

Under-sink filter

A filter plumbed into the cold-water line under your kitchen sink. Higher up-front cost, high capacity, low cost per gallon.

Pitcher filter

A jug you fill and keep in the fridge. Cheap to buy, small capacity — so the water costs the most per gallon.

Methodology & sources

Cost per gallon = each product's Amazon price ÷ its certified capacity in gallons, across 258 certified filters with published capacity, using the Amazon prices we read in July 2026. These are study figures for that date, not current prices; prices change.

Important caveat: Capacity is the manufacturer's certified rating; real-world filter life varies with how dirty your water is. Up-front price still matters on a tight budget — this compares the long-run cost of the water itself.

This study draws on 21,807 U.S. public water systems and our full certified-filter database. All EPA data is public domain.