How it works
The real cost of filtered water comes mostly from replacement cartridges. Dividing the cartridge price by its rated capacity gives a cost per gallon you can compare directly with bottled water.
The upfront price of the pitcher, faucet mount, or under-sink unit is a one-time cost, so it is added only to the first year. After that, ongoing costs are cartridges alone.
Default prices are example assumptions, not quotes. Replace them with prices from your own receipts for an accurate answer.
The formula
- Filter cost per gallon = cartridge price ÷ cartridge capacity (gal)
- Filter first-year cost = daily use × 365 × filter cost per gallon + system price
- Bottled cost per year = daily use × 365 × bottled price per gallon
- Break-even days = system price ÷ (daily use × (bottled − filter cost per gallon))
How to use this calculator
- Enter how much drinking water your household uses per day.
- Enter your cartridge price and its rated capacity in gallons.
- Enter the upfront price of the filter system.
- Enter what you pay per gallon for bottled water.
- Read the cost per gallon and first-year savings.
Frequently asked questions
Is filtered tap water cheaper than bottled water?
In most cases, yes. Cartridge costs per gallon are usually a fraction of bottled water prices, but enter your own prices to check.
Should I replace the cartridge before its rated capacity?
Follow the manufacturer's schedule, which may be based on months as well as gallons. If you replace by time, use the gallons you actually filter in that period as the capacity.
Does this include electricity or water bill costs?
No. The tap water itself costs very little per gallon compared with cartridges, so it is left out to keep the comparison simple.