For most homes, the Aquasana SmartFlow AQ-SFRO2 is the reverse osmosis system to start with. Of the four systems here, it has the broadest certified claim list: WQA lists it under NSF/ANSI 42, 53, 58 and 401, including lead and PFOA/PFOS under NSF/ANSI 53. The iSpring RCC7AK-BN is the conventional six-stage tank choice. It has an NSF-listed lead claim, uses standard 10 by 2.5-inch filters and needs no electricity. The iSpring RO500-BN is the tankless, high-output pick, and the APEC ROES-50 is a classic five-stage tank system rated for feed water up to 2,000 ppm TDS.

All four are under-sink systems that treat water at one tap. The EPA’s WaterSense guide notes that RO removes beneficial minerals such as calcium along with contaminants, does not remove all contaminants, and produces reject water. Test your water first, then pick the system whose certified claims match what you found.

Quick comparison

Product Design Certified claims (certifier) Listed daily production Filter changes (maker)
Aquasana SmartFlow AQ-SFRO2 Tank, 4 stages with remineralizer NSF/ANSI 42, 53, 58, 401, incl. lead, PFOA/PFOS (WQA) 25.7 gpd (WQA) Carbon and remineralizer 6 mo; membrane 12 mo
iSpring RCC7AK-BN Tank, 6 stages with alkaline stage NSF/ANSI 58, incl. lead, fluoride, TDS (NSF) 25.41 gpd (NSF) Five filters 6 to 12 mo; membrane 2 to 3 yr
iSpring RO500-BN Tankless, 3 stages, needs power NSF/ANSI 58, TDS only (NSF) 500 gpd (NSF) Membrane 24 to 36 mo; post-carbon up to 12 mo
APEC ROES-50 (Amazon search) Tank, 5 stages NSF/ANSI 58, TDS only (WQA) 34.8 gpd (WQA) Pre-filters 6 to 12 mo; membrane 2 to 4 yr (city)

Daily production is the rate shown in each system’s NSF or WQA listing, checked October 5, 2026. Marketed figures such as “75 GPD” or “50 GPD” are higher; APEC, for example, rates its 50 GPD figure at 60 psi.

1. Aquasana SmartFlow AQ-SFRO2: best certified claim list

The SmartFlow Reverse Osmosis uses four stages: a carbon block, Aquasana’s SmartFlow membrane, a Claryum carbon block and a remineralizer that Aquasana says adds back minerals lost in the RO process. Aquasana lists a 0.7 gpm flow rate, a 15 by 4.5 by 12.93-inch manifold and a 13.74 by 9.06-inch tank. The owner’s manual puts storage tank capacity at 2.5 gallons.

Certification status: WQA’s directory lists the AQ-SFRO2 under NSF/ANSI 58 for arsenic (V), barium, cadmium, copper, fluoride, hexavalent and trivalent chromium, nitrate, nitrite, radium 226/228, selenium, TDS and turbidity. It also lists it under NSF/ANSI 53 for asbestos, cyst, lead, mercury, MTBE, PFOA, PFOS and VOCs, and under NSF/ANSI 42 and 401. The performance data sheet gives a 42.8% recovery rating and a 27.4% efficiency rating.

Trade-offs: Aquasana rates the two carbon blocks for 250 gallons or 6 months, the remineralizer for 6 months and the membrane for 12 months, a shorter membrane interval than the multi-year figures the other three makers give. The manual sets limits of 1,000 ppm TDS, 10 grains per gallon of hardness and 40 to 80 psi supply pressure, so check your hardness result before you buy.

2. iSpring RCC7AK-BN: best for a certified lead claim with standard filters

The iSpring RCC7AK is a six-stage tank system: sediment, granular carbon and carbon block pre-filters, the RO membrane, a post-carbon filter and an alkaline stage. iSpring says that last stage adds 30 to 60 mg/L of calcium and magnesium. It uses 10 by 2.5-inch standard cartridges (per iSpring’s F9K replacement set ), runs without electricity and has a 3.2-gallon storage tank. iSpring lists product dimensions of 15.5 by 5.1 by 19.0 inches.

Certification status: NSF’s listing for iSpring shows the RCC7AK-BN under NSF/ANSI 58 with a daily production rate of 25.41 gpd and reduction claims for asbestos, barium, cadmium, trivalent chromium, copper, fluoride, lead, selenium and TDS. iSpring’s page also says the system removes PFAS, including PFOA and PFOS. That is iSpring’s claim; it is not in the NSF listing.

Trade-offs: six cartridges is more parts to stock. iSpring says to replace the five non-membrane filters every 6 to 12 months and the MC7 membrane every 2 to 3 years. Its marketed “75 GPD” is well above the 25.41 gpd in the NSF listing, and iSpring notes that flow slows if you draw more than the tank’s 3.2 gallons at once. iSpring publishes no efficiency rating on the product page. Our G3P800 vs RCC7AK comparison covers how it differs from a powered tankless unit.

3. iSpring RO500-BN: best tankless system

The iSpring RO500-BN is a three-stage tankless system: a composite sediment and carbon block filter (FCF500), the MRO500 membrane and an FCB500 carbon block. iSpring says it produces 500 gallons per day at up to 0.4 gpm, with a pure-to-drain ratio of up to 2:1. It uses built-in booster pumps, so it plugs in. Its feed adapter fits 1/2- or 3/8-inch pipes, and the system measures 17.5 by 5.12 by 16.25 inches.

Certification status: NSF lists the RO500-BN under NSF/ANSI 58 for TDS reduction only, at a 500 gpd daily production rate. iSpring’s lead and PFAS wording on the product page is the maker’s claim, not part of that listing.

Trade-offs: you need an outlet under the sink, and the certified claim list is narrow. iSpring rates the MRO500 membrane for 24 to 36 months and the FCB500 for up to 12 months. Its own pages give two different intervals for the FCF500 first stage, so follow the system’s filter service lights for that one.

4. APEC ROES-50: best for higher-TDS feed water

The APEC ROES-50 is a five-stage tank system: a sediment filter, two carbon blocks, the RO membrane and a coconut-shell carbon post-filter. APEC says it uses industry-standard parts and components and ships with a lead-free faucet and a 4-gallon pressurized tank (11 by 11 by 15 inches). It lists 40 to 85 psi feed pressure, 40 to 100°F feed temperature and a maximum of 2,000 ppm TDS.

Certification status: WQA’s NSF/ANSI 58 listing for APEC shows the ROES-50 for TDS reduction only, at 34.8 gpd. APEC’s longer list of contaminants is its own claim. The ROES-50 manual gives an 11.80% efficiency rating and a 25.40% recovery rating.

Trade-offs: its 11.80% efficiency rating is the lower of the two published here, and its five stages don’t include a remineralization filter. On upkeep, APEC’s manual calls for pre-filters every 6 to 12 months, the membrane every 2 to 4 years on city water (every 2 years on well water) and the post-filter every 2 to 4 years. We couldn’t confirm an exact ROES-50 listing sold by Amazon or APEC, so the link is a labeled search. Our ROES-50 review covers cabinet fit and pressure in more detail.

How to choose a reverse osmosis system

  • Match certified claims to your water test. All four are listed under NSF/ANSI 58, but the RO500-BN and ROES-50 are listed for TDS only. If lead, fluoride or nitrate is the reason you’re buying, choose a system whose listing names it. The EPA’s guide notes that an RO system may also be certified to NSF/ANSI 42, 53 or 55. Our certification guide shows how to read a listing.
  • Compare listed production, not marketing numbers. The listed rates here run from 25.41 to 500 gpd. Tank systems also serve water from storage; iSpring notes that the tank is what supplies pressure to the faucet on a traditional RO system.
  • Look at efficiency. The EPA estimates that a typical point-of-use RO system wastes at least five gallons for every gallon treated, and that WaterSense-labeled systems waste 2.3 gallons or less. The two published efficiency ratings here are 11.80% (ROES-50) and 27.4% (AQ-SFRO2); for the RO500-BN, iSpring publishes a pure-to-drain ratio of up to 2:1 instead. Our guides to waste-water ratio and recovery rate explain the terms.
  • Check feed limits. Supply pressure, TDS and hardness limits differ. Aquasana lists 40 to 80 psi, 1,000 ppm TDS and 10 gpg hardness for the AQ-SFRO2. APEC lists 40 to 85 psi and 2,000 ppm TDS for the ROES-50, and its manual says very hard water can clog the membrane unless a softener is added.
  • Plan the cabinet. Tank systems need room for the tank. The RO500-BN skips the tank but needs an outlet. All four send reject water to a drain line. Our RO buying guide has a full checklist.

FAQ

How much water does a reverse osmosis system waste?

The EPA’s WaterSense guide estimates that a typical point-of-use RO system sends at least five gallons of water to the drain for every gallon of treated water, and that WaterSense-labeled models send 2.3 gallons or less. Compare a system’s published efficiency rating or pure-to-drain ratio, and check the EPA’s WaterSense product search for the exact model.

Is a tankless RO system better than a tank system?

It depends on space, power and output. The iSpring RO500-BN needs an electrical outlet and uses built-in booster pumps, and iSpring rates it for 500 gallons per day. Tank systems such as the RCC7AK-BN and ROES-50 have no pump. iSpring says the RCC7AK runs without electricity, and APEC’s manual treats the ROES-50 as a non-pump system. Their storage tanks need cabinet space.

Does reverse osmosis remove PFAS?

Only a certified claim tells you. Of these four, only the Aquasana AQ-SFRO2 has PFOA and PFOS reduction in a certifier’s listing, under NSF/ANSI 53 in WQA’s directory. iSpring’s PFAS wording for its systems is the maker’s own claim, not part of the NSF listing.

Sources

Specifications and certification listings were checked on October 5, 2026. Better Water Guide has not tested these products. This is desk research, not a water-safety diagnosis.