Reverse Osmosis System for Well Water: 4 Units Compared

For a private well, an under-sink reverse osmosis (RO) system cleans drinking and cooking water at one tap. It doesn’t fix the whole house. Choose it by the NSF/ANSI 58 claim on its performance data sheet that matches your lab result, and feed it water that is already free of coliform and within its iron, hardness and pressure limits. Of the four units we compared, only the two Aquasana systems carry a certified nitrate/nitrite claim. Neither of the other two makers publishes one.

The four units compared

	Aquasana SmartFlow (AQ-SFRO2)	Aquasana HealthShield (AQ-HSRO800)	Home Master TMHP	Waterdrop G3P800
Certifier and standards	WQA: NSF/ANSI 42, 53, 58, 401; CSA B483.1	IAPMO R&T: NSF/ANSI 42, 53, 58, 372, 401	Whole system not stated (tubing NSF 51; UV EPA-registered)	IAPMO R&T: NSF/ANSI 42, 53, 58, 372
Certified nitrate/nitrite claim	Yes, up to 27 mg/L nitrate + 3 mg/L nitrite as N, at 40 psi or more	Yes, same conditions	Not stated	No (FAQ claim only)
Certified arsenic claim	Pentavalent arsenic	Pentavalent arsenic, tested at 0.050 mg/L or less	Not stated	No (FAQ claim only)
Production	25.7 gpd daily rate (51.4 gpd membrane)	800 gpd	50 gpd (75 gpd membrane optional)	800 gpd
Efficiency or drain ratio	27.4% efficiency	64% efficiency; 1.8:1	About 1:1 with permeate pump	3:1
Inlet pressure	40–100 psi (data sheet); 40–80 psi (product page)	60–125 psi	40–90 psi	Not stated
Published feed-water limits	Not stated	Not stated	2,000 ppm TDS; 10 gpg hardness; 1 ppm iron; zero iron bacteria; pH 4–10; 5 NTU	Not stated
Power	None	120 V outlet within 6 ft	Standard outlet for the UV LED	Power adapter included
Storage	3.2 gal tank	Tankless	3.2 gal tank	Tankless
Relative cost	$	$$$	$	$$

Sources: each manufacturer’s product page and, for Aquasana, its performance data sheets.

What well water needs ahead of an RO unit

City water arrives disinfected, softened in some areas and at steady pressure. Well water often has none of that, and an RO membrane is sensitive to all three.

Bacteria: feed it coliform-free water

Nebraska Extension says an RO membrane can remove microorganisms but should not be used for that. Only coliform-free water should go in, because bacteria degrade the membrane and can get through pinhole leaks. Connecticut’s health department and Georgia Extension also say RO alone is not a bacteria treatment. Aquasana’s own pages say a UV filter has to be added for bacteria and viruses. If your last test was positive, start with coliform in well water, then look at whole-house UV units.

Hardness, iron, manganese and turbidity

Connecticut’s health department lists turbidity, iron, manganese, hydrogen sulfide and chlorine as things that reduce RO performance. It says particulate iron can clog the membrane, so a point-of-entry treatment may be needed first. Nebraska Extension says a softener ahead of the unit can extend membrane life on relatively hard water. Home Master is the only maker here that gives numbers: 10 gpg hardness, 1 ppm iron, zero iron bacteria and 2,000 ppm TDS. Above those, it offers a high-hardness membrane rated to 18 gpg. If your water is past any of those limits, treat it at the point of entry first. Our well water treatment system guide explains the order.

Carbon prefilters on unchlorinated water

Nebraska Extension says that if the feed water is not chlorinated, a carbon prefilter can encourage microbial growth on the membrane, and it recommends a sediment-only prefilter in that case. Each unit here pairs its membrane with carbon cartridges. That doesn’t disqualify them, but change the prefilters on the maker’s schedule and disinfect the system as the manual directs.

Pressure and cold water

The certified nitrate claims on both Aquasana data sheets apply only to supplies at 40 psi or more. A jet-pump system on a 30/50 pressure switch spends part of every cycle below that. Connecticut recommends a booster or permeate pump to keep RO pressure above about 40 psi. Cold water also cuts production. Nebraska Extension gives a 1–2% drop in output for every degree below 77°F, and says 45°F well water makes about half as much.

Wastewater and the septic system

Connecticut’s health department treats 30 gallons a day or less of RO reject water to a septic system as incidental, and says larger flows may cause problems. A higher-efficiency unit or a permeate pump sends less water to the drain.

Nitrate and arsenic: read the performance data sheet

The EPA’s limits are 10 mg/L for nitrate (as nitrogen) and 0.010 mg/L for arsenic. A marketing list of “contaminants reduced” doesn’t tell you a unit will meet either one on your water. The performance data sheet does.

• Nitrate. Both Aquasana data sheets limit the certified claim to feed water with no more than 27 mg/L nitrate plus 3 mg/L nitrite (as N), at 40 psi or more. Removal is a percentage, so high feed levels matter. In Nebraska Extension’s example, a membrane rejecting 85% takes 40 mg/L of nitrate down to 6 mg/L, but 80 mg/L only down to 12 mg/L, still over the limit. Our nitrates in well water guide covers testing and the infant-health advice.
• Arsenic. Georgia Extension notes that an NSF arsenic claim for RO covers only arsenic V (pentavalent), not arsenic III. The HealthShield data sheet says the same. It is meant for water with a free chlorine residual at the inlet, or water shown to contain only pentavalent arsenic. Most wells are not chlorinated, so you would need a lab result for the arsenic form before relying on either Aquasana claim.

The picks

Aquasana SmartFlow (AQ-SFRO2): best fit for nitrate where pressure stays at 40 psi or more

WQA certifies it to NSF/ANSI 58 for nitrate/nitrite and pentavalent arsenic, and the operating range starts at 40 psi. It uses no electricity and stores water in a 3.2 gal tank. Production is low: the data sheet gives a 25.7 gpd daily rate and 27.4% efficiency, so most of the feed water goes to drain. Warranty is 2 years.

Aquasana HealthShield (AQ-HSRO800): for high-demand households

It makes 800 gpd with no tank and has the best rated efficiency here, at 64%. Its IAPMO R&T certification covers nitrate/nitrite, pentavalent arsenic and five PFAS compounds. The catches are a 120 V outlet within 6 ft, a 60–125 psi operating range, and a Stage 1 cartridge rated for 6 months or 320 gallons. Confirm with Aquasana how that pressure range applies on a 30/50 or 40/60 well system before buying. It costs the most of the four.

Home Master TMHP: most complete published feed-water limits

This is the only unit whose maker tells a well owner what feed water it can take. It includes a KDF85 iron prefilter, a 5-micron sediment prefilter, a non-electric permeate pump (about 1:1 waste ratio) and a UV LED stage that needs an outlet. Warranty is 5 years. The cons: the page names NSF 51 tubing and an EPA-registered UV, but not a whole-system NSF/ANSI 58 certification, and it lists feed pressure two ways (40–90 psi and 40–95 psi).

Waterdrop G3P800: for fluoride and PFOA/PFOS, not nitrate

It makes 800 gpd tankless with a 3:1 pure-to-drain ratio, and its IAPMO R&T certified claims cover fluoride, TDS, chromium, chlorine and PFOA/PFOS. Nitrate and arsenic appear only in the FAQ, outside the certified claims. The page gives no feed-pressure, temperature or feed-water limits, and the warranty is 1 year.

How to choose

1. Start from a lab report. Nebraska Extension and Connecticut’s health department both say to test before choosing equipment. See well water treatment systems for what to test.
2. Match the certified claim to the contaminant. For nitrate or arsenic, only a performance data sheet claim under NSF/ANSI 58 counts, along with its concentration and pressure conditions.
3. Check your pressure switch against the unit’s minimum. If the cut-in is below the unit’s minimum, plan on a booster or permeate pump.
4. Clear the feed-water hurdles first. That means coliform, hardness, iron, manganese and turbidity.
5. Retest after installation. Connecticut recommends testing both raw and treated water at a certified lab after installation, then at least once a year.

For the rest of the house, see our whole-house water filter guide.

Who should skip all of these

• Wells that test positive for coliform and have not been disinfected and retested. RO is not the fix.
• Whole-house problems like staining, scale or rotten-egg odor. These units treat one faucet. Nebraska Extension notes that dissolved gases such as hydrogen sulfide pass through the membrane.
• Nitrate above the certified range. If your result is above 27 mg/L nitrate plus 3 mg/L nitrite as N, no unit here is certified for your water. Talk to your state health department about the source and other options.

Sources

1. Aquasana — SmartFlow Reverse Osmosis (AQ-SFRO2) product page
   Stages, 51.4 gpd membrane, 0.7 gpm, 40–80 psi, 40–100°F, 3.2 gal tank, UV needed for bacteria and viruses
2. Aquasana — AQ-SFRO Performance Data Sheet
   WQA certification; nitrate/nitrite and pentavalent arsenic claims; 27 + 3 mg/L as N and 40 psi conditions; 27.4% efficiency; 25.7 gpd; 40–100 psi
3. Aquasana — HealthShield Tankless Reverse Osmosis (AQ-HSRO800) product page
   800 gpd, 0.56 gpm, 1.8:1, 120 V within 6 ft, filter intervals, UV needed for bacteria and viruses
4. Aquasana — AQ-HSRO800 Performance Data Sheet
   IAPMO R&T certification; 60–125 psi; 64% rated efficiency; arsenic V scope and free-chlorine condition; nitrate/nitrite conditions
5. The Perfect Water (Home Master) — HydroPerfection TMHP product page
   Feed limits (TDS, hardness, iron, iron bacteria, pH, 5 NTU), feed pressure, permeate pump, UV LED, warranty
6. Waterdrop — G3P800 Tankless Reverse Osmosis System product page
   800 gpd, 3:1, IAPMO R&T certified claims, filter life, warranty
7. University of Nebraska–Lincoln Extension — Drinking Water Treatment, Reverse Osmosis (G1490, rev. 2014)
   Coliform-free feed only; carbon prefilters on unchlorinated water; 1–2% output loss per °F below 77°F; softener extends membrane life; 85% rejection example
8. Connecticut Department of Public Health — Reverse Osmosis Treatment of Private Drinking Water Systems (Publication 21)
   Turbidity, iron, manganese, H2S and chlorine affect RO; 30 gal/day reject to septic; booster or permeate pump; retest after install
9. University of Georgia Extension — Water Quality and Common Treatments for Private Drinking Water Systems (B 939)
   NSF arsenic claim for RO covers arsenic V, not arsenic III; RO not for bacteria
10. EPA — National Primary Drinking Water Regulations
    Nitrate MCL 10 mg/L as N; arsenic MCL 0.010 mg/L