HomeWaterMath

Water filter calculators

A filter removes things from your water; a softener removes hardness. Which filter you need depends on what's in your water, so start with a test from a certified lab or your utility's yearly water quality report.

The calculators here price the two most common choices: an under-sink reverse osmosis system for drinking water, and a whole house filter for every tap. Both include the running costs that make up much of the real price: cartridges, media changes and, for reverse osmosis, the water sent to the drain.

Which calculator do I need?
If you want to knowUse
Drinking and cooking water onlyReverse osmosis system cost
Chlorine taste and smell at every tapWhole house water filter cost
Well water with sediment, iron or sulfurWhole house water filter cost
Hard water and scaleWater softener cost
Chrome kitchen faucet over a stainless steel double sink
Reverse Osmosis System Cost Calculator 

Under-sink, tankless or countertop, with filters and water sent to drain.

Water falling from a round rain shower head
Whole House Water Filter Cost Calculator 

Cartridge, carbon tank or well system, with media changes for your use.

Gloved hands fitting a threaded pipe connection during an installation
Water Softener Cost Calculator 

Unit, install, salt and service, with a 10-year total and a quote check.

FAQ

What's the difference between a water filter and a water softener?
A softener swaps hardness minerals for sodium or potassium so scale doesn't form. A filter removes other things, such as sediment, chlorine, lead or bacteria, depending on its type. Many homes on hard water use both.
Do I need a whole house filter or an under-sink filter?
If the problem is taste, smell or sediment at every tap, a whole house filter. If you only want cleaner drinking and cooking water, an under-sink filter or reverse osmosis system is cheaper.
Should I test my water before buying a filter?
Yes. On city water, read your utility's annual water quality report. On a well, test at least once a year with a certified lab.
Sikander Mushtaq

Founder of HomeWaterMath. Builds and checks every calculator.

Last updated: Oct 21, 2026 · Editorial policy