APEC ROES-100
#1 in With tankFull review
For families who want a certified tank RO system with more output and a faster pour than entry models, at a low price.
Amazon $199.99$199.99
An under-sink reverse osmosis system pushes tap water through a membrane fine enough to hold back dissolved salts, metals and most other contaminants, then sends what it rejects down the drain. It feeds its own small faucet beside the kitchen tap. These rankings compare what the makers and the certifiers publish on the same terms: whether the system is certified, what its filters cost to keep up, how much water it wastes, how much it makes, what it costs and how long it’s covered.
Tank or tankless is the first choice. A tankless system has a pump that filters on demand, so it fills a glass in seconds, wastes less water and frees up cabinet space, but it needs an outlet under the sink. A tank system slowly fills a storage tank of a few gallons using house water pressure alone; it costs less and needs no power, but the tank can run low when you fill a big pot.
Certification is the second. NSF/ANSI 58 is the standard for reverse osmosis systems, and a listing from NSF, WQA, IAPMO or CSA means an independent lab tested that exact model. Many makers say a system is “tested to” or “meets” the standard, which is not the same thing, and some systems are certified only for lead-free materials (NSF/ANSI 372).
Filter cost is the third. Over a few years the replacement filters and membranes cost more than the system itself, and the yearly cost ranges from under $100 to over $300 depending on the model.
Top Picks
iSpring RCC7
#2 in With tankFull review
For a household that wants proven, certified RO water at a low price and does not mind a tank under the sink. Filters cost little and are easy to find.
Amazon $188.09$188.09
Waterdrop G5P500A
#1 in TanklessFull review
For a buyer on a budget who still wants certified RO water with minerals added back.
Amazon $229.99$229.99
Shop by Type
Tankless
15 rankedCompact systems with a pump that filter on demand: more cabinet space and less water wasted.
Top rated: Waterdrop G5P500A $229.99
With tank
14 rankedClassic systems that fill a storage tank: no power needed, cheaper filters, a slower refill.
Top rated: APEC ROES-100 $199.99
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Deals
Prices were last checked November 2, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Best Tankless Reverse Osmosis Systems
- Waterdrop G5P500A#1 of 15Full review
For a buyer on a budget who still wants certified RO water with minerals added back.
Amazon $229.99$229.99500 gpd2:1$125 a year - Waterdrop G5P700A#2 of 15Full review
For a buyer who wants certified RO with mineralized water and a smart faucet for around $300.
Amazon $309.99$309.99700 gpd2:1$130 a year - Delta Clarifi Tankless RO#3 of 15Full review
For a household that wants a broadly certified tankless system with low running costs and a long warranty. Budget buyers can get similar output for less.
Amazon $799$799600 gpd2:1$201 a year - Waterdrop G3P600#4 of 15Full review
For a household that wants a certified tankless RO system with a smart faucet at a mid-range price. Its NSF 58 listing is the main reason to pick it over cheaper tankless units.
Amazon $439$439600 gpd2:1$145 a year - Waterdrop X12#5 of 15Full review
For a large household that wants the fastest flow and lowest waste, and will pay a premium for it.
Amazon $1,099$1,0991,200 gpd3:1$173 a year
Best Reverse Osmosis Systems With a Tank
- APEC ROES-100#1 of 14Full review
For families who want a certified tank RO system with more output and a faster pour than entry models, at a low price.
Amazon $199.99$199.99100 gpd1:1$95 a year - iSpring RCC7#2 of 14Full review
For a household that wants proven, certified RO water at a low price and does not mind a tank under the sink. Filters cost little and are easy to find.
Amazon $188.09$188.0975 gpd-$63 a year - APEC RO-90#3 of 14Full review
For buyers who want a certified, low-maintenance tank RO system with long-lasting filters.
Amazon $209.99$209.9990 gpd-$73 a year - APEC RO-Hi#4 of 14Full review
For cooks and families who fill pots and pitchers often and want a faster pour from a certified tank system.
Amazon $299.94$299.9490 gpd-$73 a year - iSpring RCC7AK#5 of 14Full review
For buyers who want certified RO water with minerals added back for taste, at a low price. Choose a tankless system instead if cabinet space or wasted water matters more.
Amazon $199.99$199.9975 gpd-$95 a year
How We Rank
Each system is ranked against others of the same type, and scored on its NSF/ANSI 58 certification, what its replacement filters cost a year, how much water it sends to the drain, its rated output, its price and its warranty.
| Factor | Measures | Weight |
|---|---|---|
| Certification | certified to NSF/ANSI 58 for reverse osmosis | 25% |
| Filter cost | replacement filters a year | 20% |
| Water wasted | drain water per gallon of purified water | 15% |
| Output | rated gallons a day | 10% |
| Price | price of the system | 15% |
| Warranty | warranty length | 15% |
How we rank explains each factor in full.