Reverse Osmosis System Cost Calculator

How to use this calculator

Choose the type of system and who will install it.
Enter your household. One gallon per person a day covers drinking and cooking for most homes.
Choose the efficiency. If the box shows a WaterSense label, choose that; if the maker lists a drain ratio, enter it.
Add your water rate to price the drain water, and tick any extras your kitchen needs.

The formula

10-year cost = upfront cost + 10 × (filters + water sent to drain)

Water sent to drain = RO water × drain ratio. A system that's 15% efficient sends about 5.7 gallons to the drain for every gallon you drink. At the 30% WaterSense minimum, that falls to about 2.3 gallons.

Example 1: under-sink with tank, plumber, family of 4, standard efficiency, water at $12 per 1,000 gallons. Upfront is $300 to $700, typically $500. The family makes 1,460 gallons of RO water a year and sends 8,273 gallons to the drain, about $99 of water. With $50 of filters, that's $149 a year and $1,993 over 10 years, about 13.6¢ per gallon. A WaterSense-labeled system would send 3,407 gallons ($41) and total $1,409.

Example 2: tankless with a 1:1 drain ratio, plumber, fridge line added. Upfront is $525 to $1,080, typically about $803. With $50 of filters a year, 10 years costs about $1,303 (8.9¢ per gallon), before any water charge.

(Display rule: typical dollars are rounded to whole dollars, so $802.50 shows as $803 and the 10-year total as $1,303.)

What this calculator doesn't cover

Whole-house reverse osmosis. It's a different system: $1,000 to $4,800 installed per This Old House and Angi, or $4,800 to $8,000 per HomeGuide, plus pumps, storage and often a softener in front.
Remineralization or UV add-on stages.
Booster pumps for low water pressure (needed below about 40 to 45 psi).
Bottled water you'd stop buying.

Reverse osmosis cost by type

Type	Unit only	Installed
Under-sink with tank	$150 to $350	$300 to $700
Tankless under-sink	$300 to $600	$450 to $950
Countertop	$200 to $700	no install
Whole-house	n/a	$1,000 to $8,000

HomeGuide (2025), Angi (2026), This Old House (2026). Sources disagree on whole-house RO; the range covers both.

Filter schedule

Stage	How often	Typical cost
Sediment and carbon pre-filters	every 6 to 12 months	about $30 a set
RO membrane	every 2 to 4 years	$30 to $100
Carbon post-filter	every 12 months or with the membrane	included in most sets

APEC and Express Water filter pages (Oct 2026); Angi (2026).

Water sent to drain per gallon of RO water

System	Efficiency	Gallons to drain
Typical older under-sink	10 to 20%	about 4 to 9
WaterSense labeled (tank)	30% or better	2.3 or less
High-efficiency tankless (maker claims)	25 to 50%	about 1 to 3

EPA WaterSense specification and supporting statement for RO systems (Nov 2024); maker figures vary, check the spec sheet.

Tips

Test your water first. RO is great for nitrate, arsenic, PFAS and dissolved solids, but you don't need it for chlorine taste alone; a carbon filter does that.
Look for the WaterSense label. It means the system wastes less water and is certified to NSF/ANSI 58.
Low water pressure slows output and raises waste. Below about 40 psi, ask about a booster pump.
Buy filters as yearly sets. They're cheaper than single cartridges and easier to keep on schedule.
If your countertop is stone, ask the installer to use the existing sprayer or soap hole for the RO faucet and skip drilling.

FAQ

How much does a reverse osmosis system cost?

Most under-sink systems cost $150 to $350 for the unit and $300 to $700 installed. Tankless models cost $300 to $600, or $450 to $950 installed. Whole-house systems cost $1,000 to $8,000 installed depending on the source and system.

How much does it cost to maintain a reverse osmosis system?

About $50 to $100 a year for filters. Pre-filters are changed every 6 to 12 months and the membrane every 2 to 4 years.

How much water does reverse osmosis waste?

EPA says typical point-of-use systems run at 10 to 20% efficiency, which sends about 4 to 9 gallons to the drain for each gallon of filtered water. WaterSense-labeled systems must be at least 30% efficient, about 2.3 gallons or less.

Is reverse osmosis worth it?

If your water has nitrate, arsenic, lead, PFAS or high dissolved solids, it's one of the most effective home options. For a family of 4 it works out to roughly 7 to 14 cents per gallon over 10 years, including filters.

Can I install a reverse osmosis system myself?

Yes, most under-sink systems are made for DIY install with basic tools. A plumber typically charges $150 to $350 and more if you need a new drain line or a fridge line.

Do I need whole-house reverse osmosis?

Rarely. Most homes only need RO water for drinking and cooking, so an under-sink system is enough.