Quick Answer: An under-sink reverse osmosis system costs $300 to $1,300 installed, with most homeowners landing near $350-$500 for a straightforward job, according to 2026 cost data from HomeGuide and ThisOldHouse. A basic tank-based unit like the APEC ROES-50 runs about $199 for the unit itself, while tankless systems like the Waterdrop G3P800 run $699-$999 - several times more upfront, but with far less water waste per gallon produced. Annual upkeep after that runs $50-$250, driven mostly by how often you replace the membrane (every 2-3 years).
Every RO system review on this site ranks units by purity, flow, and waste ratio - this guide is the piece that comes after: what the total cost looks like once installation and the ongoing filter changes are added to the sticker price.
Reverse osmosis cost, by system type
Real 2026 pricing splits cleanly into three tiers depending on what you’re buying and how it’s installed:
- HomeGuide’s 2026 cost data puts a typical under-sink RO install at $300-$950, with complex jobs (new water line, drilling a stone countertop) pushing labor alone to $500-$900.
- ThisOldHouse puts the full range wider, at $150-$1,300 total - materials $50-$1,000 plus labor $150-$300 for a standard install.
- Angi’s often-cited “$2,200 average” blends point-of-use and whole-house RO jobs together in one number ($1,000-$4,800 stated range) - quoting that figure for an under-sink system alone overstates the real cost by several times, so it’s worth reading past the headline average.
| System type | Unit cost | Installed total | Annual upkeep |
|---|---|---|---|
| Tank-based RO (under-sink) | $150–$600 | $300–$950 | $40–$120 |
| Tankless RO (under-sink) | $400–$1,200 | $600–$1,300 | $60–$150 |
| Whole-house RO | $3,500–$6,500 | $4,800–$8,000+ | $200–$500 |
Tank vs. tankless: the real price gap
Tank-based systems cost less because the tank itself does the work of storing pressurized water for instant use, so the membrane can run slowly in the background. A tank unit like the APEC ROES-50 lists around $199, and the iSpring RCC7AK around $219 - both real current prices, not estimates. Tankless systems replace that storage tank with a faster membrane and a pump, delivering filtered water on demand instead of from a reservoir. That’s why the Waterdrop G3P800 runs $699-$999 and the iSpring RCS5T around $600-$608 - two to four times the price of a comparable tank system for the same core filtration.
The tradeoff isn’t just price. Older tank RO systems waste roughly 3-4 gallons down the drain for every gallon of clean water produced; tankless systems like the G3P800 cut that closer to 1:1. If your water bill or drain capacity matters, that efficiency gap can offset some of the higher upfront cost over time. See our full reverse osmosis system rankings for how these specific units compare on purity and flow, not just price.
APEC ROES-50 Reverse Osmosis System
The tank-based system most of the "budget tier" pricing above is built around - five stages, a standard storage tank, and one of the lowest costs per gallon of purified water in a full RO setup. Full writeup in our best reverse osmosis system guide, including how it compares to the Waterdrop G3P800 and iSpring RCC7AK.
Check price on Amazon →Replacement prefilters and membranes on time, every time - Prime ships them free in two days, so a scheduled cartridge swap doesn’t turn into two weeks of drinking un-filtered tap water while you wait on shipping. Try Prime free for 30 days.
What actually drives the installation cost
The unit price is rarely what makes an RO install expensive - it’s what the installer finds under the sink. Per ThisOldHouse’s 2026 breakdown, the real cost drivers are:
- Shutoff valve condition. A seized, corroded, or missing shutoff valve adds labor before the system installation even starts.
- Countertop material. Drilling a granite or quartz countertop for the air-gap faucet is one of the single biggest line-item cost adders in the whole job.
- Drain line distance. The drain saddle needs to sit above the P-trap and clear of the garbage disposal outlet. If there’s no existing line close enough to tap into, running a new one can add $300-$800 on its own.
A “$200 system” can quietly become an $800-$1,500 job purely because of an old valve or a stone counter - independent of which RO unit you actually buy. Ask about all three before booking an installer, not after the quote arrives.
Whole-house RO: a different tier entirely
Whole-house reverse osmosis isn’t a bigger version of the under-sink system - it’s a different category of cost. Per Angi and Forbes’ 2026 data, basic whole-house RO systems start around $1,000-$4,800, and full-size, high-output units used to treat every tap in a home run $4,800-$8,000+ - roughly 5-10x an under-sink setup, because the system needs a much larger membrane array, a permeate pump or booster, and a drain line sized for the whole house instead of one kitchen tap. Most homes don’t need it: a point-of-use system at the kitchen sink handles drinking and cooking water, which is where nearly all RO demand actually is. If chlorine taste or sediment across the whole house is the concern instead of drinking-water purity specifically, our whole house water filter cost guide covers that lower-cost, non-RO path.
Annual maintenance costs
Budget $50-$250 a year, and the split between tank and tankless is smaller than the upfront price gap suggests:
- Tank-based systems run $40-$120 a year for pre/post-filter cartridges, changed roughly every 6-12 months depending on water quality.
- Tankless systems run a bit more, $60-$150 a year, since their higher-flow cartridges cost more per swap even on a similar schedule.
- The membrane is the expensive part either way - $30-$100 to replace, but only needed every 2-3 years regardless of tank or tankless. Swap it on that schedule rather than waiting for output to visibly drop; a spent membrane lets more dissolved solids through well before flow noticeably slows.
The bottom line
Budget $300-$500 all-in for a basic tank-based under-sink system like the APEC ROES-50 with a straightforward install, or $600-$1,300 for a tankless system that wastes less water and delivers faster. Whole-house RO is a separate tier at $4,800-$8,000+ and overkill for most homes chasing better drinking water rather than whole-house treatment. Before booking an installer, check your shutoff valve, countertop material, and drain-line distance - those three things move the price far more than which RO brand you pick. See our full best reverse osmosis system rankings for the specific units these numbers are based on, or our whole house water filter cost guide if whole-home treatment - not just drinking water - is the actual goal.
Prices are approximate and change often - tap the button above to check the current Amazon price.