This guide is written by Echo Water, which makes the ECHO RO, a tankless under-sink reverse osmosis system. We've tried to make the criteria useful whichever system you choose. Where we describe the ECHO RO, we use only what Echo publishes, and we point out where it falls short of our own checklist.
Short answer: the best under sink reverse osmosis system is one that fits your cabinet and plumbing, is certified to NSF/ANSI 58 for the contaminants you care about (or can show you a performance data sheet), sends as little water to the drain as possible, and has replacement filters you're willing to buy on schedule. Check your water first. If chlorine taste is your only complaint, a simpler carbon filter may be all you need.
What an under-sink RO system does
Reverse osmosis pushes water through a semi-permeable membrane that holds back most dissolved solids. A typical under-sink system has several stages: a sediment filter to catch particles, a carbon filter to reduce chlorine and protect the membrane, the RO membrane itself, and a final carbon "polishing" filter for taste. The rejected dissolved solids go down the drain in a concentrate stream, and the purified water goes to a dedicated faucet next to your main one.
Because it works at one tap, an under-sink RO system is for drinking and cooking water. It doesn't treat your shower, laundry or water heater; that's a job for a whole house water filter.
Do you actually need reverse osmosis?
RO makes the most sense when your water has dissolved contaminants that carbon alone doesn't handle well, such as nitrate, fluoride, arsenic or high total dissolved solids (TDS). City water customers can check their utility's annual water quality report (the Consumer Confidence Report, sent by July 1 each year) or use Echo's free water quality analysis by ZIP code. Private well owners should start with a certified lab test; see our guide to choosing a water filter for well water.
One trade-off to know up front: RO doesn't distinguish minerals from contaminants, so it reduces calcium and magnesium along with everything else. Some people like the clean taste; others add minerals back.
9 things to check before you buy an under sink reverse osmosis system
1. NSF/ANSI 58 certification, or a performance data sheet
NSF/ANSI 58 is the standard for reverse osmosis drinking water systems. A certified system comes with a performance data sheet listing each contaminant it was tested against and the results. Check the listing in the certifier's public database, and make sure the contaminants you care about are on it. A general percentage with no contaminants named is not the same thing.
2. Tank or tankless
Conventional RO fills a pressurized storage tank, often a sphere of a few gallons that takes up much of the cabinet, and the tap slows as the tank empties. Tankless RO purifies on demand, so it's smaller and doesn't store water, but it needs a power outlet under the sink to run.
3. Flow rate at the faucet
Look for the flow at the tap in liters or gallons per minute, not just a gallons-per-day production figure. It decides how long it takes to fill a pot.
4. How much water goes to the drain
Every RO system sends some water to the drain. Ask for the pure-to-drain ratio and the conditions it was measured under; older designs commonly run 3:1 or 4:1, and newer ones can be much closer to 1:1. Your water pressure, temperature and TDS all affect the real number.
5. Cabinet fit
Measure width, height and depth, and remember the garbage disposal, drain trap and any shelves. Check whether filters change from the front or need space above or below the unit.
6. Installation needs
- A cold water supply connection
- A drain connection, usually a saddle clamp on the sink drain
- A hole in the countertop or sink deck for the dedicated faucet (an unused soap dispenser or sprayer hole often works)
- A power outlet, for tankless or pumped systems
7. Filter intervals and annual cost
Get the replacement interval and price for every stage, including the membrane, and add up a year's worth. Filter-life indicators help, but you still need to budget for the filters.
8. Remineralization and taste
If you don't like the taste of low-mineral water, check whether the system offers a remineralization stage or whether you'll add mineral drops.
9. Leak protection, warranty and returns
An under-sink system lives in a closed cabinet, often above a wood floor. A leak detector with an automatic shutoff valve is worth considering. Check the warranty length, what it covers, and how long you have to return the system if it doesn't fit.
How to check an RO system yourself
- A handheld TDS meter is useful for RO. Measure your tap water and your RO water; the gap shows the membrane working. A reading that creeps up over time can mean the membrane needs replacing.
- A TDS meter can't measure specific contaminants such as lead, arsenic, nitrate or PFAS. For those, send before-and-after samples to a certified lab.
- Time how long it takes to fill a one-liter bottle, and compare it with the published flow rate.
Red flags when shopping for an under-sink RO system
- A contaminant-reduction percentage with no named contaminants, test standard or certifier behind it.
- A certification you can't find in the certifier's listings.
- No published drain ratio, or a ratio with no test conditions.
- No replacement filter prices or intervals.
- Health or disease promises. RO reduces specific contaminants; it isn't a treatment for anything.
How the ECHO RO measures up
Here's how the ECHO RO compares with the checklist, using only what Echo publishes. Prices are list prices on echowater.com as of September 28, 2026.
| Criterion | ECHO RO (Echo's published information) |
|---|---|
| Design | Tankless, 4 stages: sediment, carbon block, RO membrane (0.0001 micron) and post carbon. |
| Designed to reduce | Echo lists chlorine and chloramine, lead, fluoride, heavy metals, nitrates and sulfates, TDS, and taste and odor. |
| Flow rate | 1.2 L/min, made on demand. |
| Drain ratio | Roughly 1:1. Echo notes that drain ratio, cartridge life and contaminant reduction vary with source water chemistry, pressure and usage. |
| Size | 17.75 in wide x 16 in tall x 4.25 in deep; Echo recommends 5 in of clear cabinet depth. |
| Installation | Cold supply tee, drain saddle valve, standard outlet and a dedicated faucet. Echo estimates about two hours for most kitchens, or about 30 minutes for a plumber. |
| Filter changes | Sediment and carbon block every 6–12 months, post carbon about every 12 months, membrane every 2–3 years, depending on source water. Quarter-turn cartridges, no tools; a digital display shows cartridge life for each stage. |
| Filter prices | Complete set $199.99 ($169.99 on subscription); sediment, carbon block or post carbon $39.99 each; membrane $119.99. See Echo RO Filters. |
| Price | $699.99 without a faucet; $799.98 with a chrome, stainless or matte black faucet. |
| Warranty and returns | 5-year warranty, 60-day money-back guarantee, free shipping in the contiguous US. |
| Add-ons | Echo Guard leak detection kit (RO 3/8" version) and the Echo RO/Flow Faucet. |
Where the ECHO RO doesn't tick every box
- The product page doesn't list an NSF/ANSI 58 certification or a contaminant-by-contaminant performance data sheet. By our own checklist, ask Echo for test data on the contaminants that matter to you before you buy.
- It needs a power outlet under the sink. If your cabinet doesn't have one, budget for an electrician.
- Like any RO system, it reduces minerals, and its four stages don't include remineralization. Echo notes that some owners add mineral drops.
- It's one tap. For every tap in the house, see Echo's reverse osmosis systems, which include the Whole Home RO System for city water.
- As of September 28, 2026, the product page lists the ECHO RO on back order with an expected ship date of October 2026.
If the ECHO RO fits your checklist, see it with the rest of Echo's under sink and kitchen water systems.
Frequently asked questions
Is an under sink reverse osmosis system worth it?
It is if your water test shows dissolved contaminants that carbon doesn't handle well, or high TDS, and you want better drinking and cooking water at one tap. If your only issue is chlorine taste, a carbon filter costs less to buy and run.
How much water does an RO system waste?
It depends on the design and your water. Older systems commonly send 3 to 4 gallons to the drain for every gallon of drinking water; more efficient designs are closer to 1:1. Ask for the ratio and the test conditions.
How often do RO filters need changing?
Pre- and post-filters are commonly changed every several months to a year, and membranes every couple of years, depending on water quality and use. Follow the manufacturer's schedule and watch your TDS readings.
Is tankless RO better than RO with a tank?
Tankless systems save cabinet space and don't store water, but they need power. Tank systems work without power and can deliver a burst of stored water, but the tank takes up room and the flow drops as it empties. Choose based on your cabinet and how you use water.
Can I install an under-sink RO system myself?
Many people do, if they're comfortable connecting to the cold water line and drain and drilling or using a spare faucet hole. If you're unsure, a plumber can usually do it quickly. Check your local plumbing code.
Sources behind this guide
- EPA: Consumer Confidence Reports (annual water quality reports)
- EPA: National Primary Drinking Water Regulations
- NSF: Certified drinking water treatment units listings
Written by Echo Water. Last reviewed September 28, 2026. This is general information, not a substitute for a certified water test or advice from a licensed plumber.
