Reverse Osmosis for Well Water: At the Kitchen Tap, for the Right Contaminants

When a well needs reverse osmosis

A reverse osmosis (RO) unit pushes water through a membrane that holds back most dissolved substances. Minnesota lists arsenic, nitrate, nitrite, fluoride, sodium, uranium, radium and lead among what it is designed to remove¹. Those are the reasons to buy one on a well:

RO and well water contaminants · what the sources say

Contaminant	What the sources say
Nitrate	RO rejects about 83 to 92% of incoming nitrate (Penn State)2. High nitrate can still exceed the limit after treatment3
Arsenic	Works much better on arsenate (As V) than arsenite (As III); As III may need to be oxidized first4
Uranium	RO removes it effectively, but no home device is certified for uranium5
Fluoride	Certified devices use RO or distillation6

Limits to know: Health Canada’s arsenic maximum is 0.01 ppm0.01 mg/L⁷. It proposed 0.01 ppm0.01 mg/L in 2025; that consultation closed in May 2025 and the change was not final as of November 2026⁸. Nitrate’s limit is 10 mg/L as nitrogen in both countries⁷.

What RO is not for

• Bacteria. Nebraska Extension says only coliform-free water should go into an RO system: membranes can develop pinhole leaks³. Fix the well, shock chlorinate, add UV if needed, then RO.
• Hydrogen sulfide. It is a gas, and Nebraska Extension says it passes through the membrane³. See our sulfur filter guide.
• The whole house. Health Canada: “RO systems should only be installed at POU as the water they have treated may be corrosive to internal plumbing components”⁵.

The certification trap

NSF/ANSI 58 certifies each claim separately. On NSF’s own listing, many models carry only “TDS Reduction”⁹, which says nothing about nitrate or arsenic. Here is what the four units in our catalogue are actually listed for:

Under-sink RO units · certified claims, checked on the certifier's listing

Unit	Nitrate	Arsenic (V)	Fluoride	Listing
Aquasana SmartFlow AQ-SFRO2	Yes	Yes, 50 ppb	Yes	WQA10
APEC RO-90	No	Yes, 300 ppb	Yes	WQA10
Waterdrop G3P600	No	No	Yes	IAPMO11
iSpring RCC7AK	No	No	No (TDS only)	NSF9

Two more details from the listings. Arsenic claims hold only for water at or below the tested level and valence⁹, and the test assumes a free chlorine residual, which well water usually lacks⁴. And the Waterdrop manual makes its warranty conditional on municipal tap water and hardness under 7 gpg¹², which rules out many wells.

Units certified for well contaminants

Under-sink RO, nitrate and arsenic

Aquasana SmartFlow Reverse Osmosis (AQ-SFRO2)

NSF/ANSI 58 (WQA)

Certified for

nitrate/nitrite, arsenic V (50 ppb), fluoride, radium, lead (53), TDS

Nitrate limit

up to 27 mg/L nitrate-N + 3 nitrite-N, at 40 psi or more

Production

25.7 gal/day

Efficiency

27.4% (about 2.6 gal to drain per gal, our calculation)

Hardness

under 10 gpg

Strengths

• The only unit in our catalogue certified for nitrate
• Also certified for pentavalent arsenic and fluoride
• Includes a nitrate test strip; maker says test every 3–4 months

Drawbacks

• Nitrate claim only at 40 psi or more and up to the tested level
• Removes arsenic V only, not arsenic III
• Needs hardness under 10 gpg: soften first on hard wells

Good fit: a well with nitrate, pentavalent arsenic or fluoride at the kitchen tap.
Skip it if: water pressure under 40 psi, or arsenic III without pre-oxidation.

Under-sink RO, higher arsenic

APEC Ultimate RO-90

NSF/ANSI 58 (WQA)

Certified for

arsenic V (300 ppb), fluoride, radium, lead, TDS

Not certified for

nitrate

Production

90 gal/day (maker)

Pressure

40–85 psi (warranty table)

Membrane life

2–3 years on well water (maker)

Strengths

• Certified for pentavalent arsenic up to 300 ppb
• No electricity needed
• Maker gives a separate membrane life for well water

Drawbacks

• No nitrate certification, despite the maker's page listing nitrate
• Waste ratio not published
• 1-year warranty

Good fit: a well with pentavalent arsenic or fluoride, and no nitrate problem.
Skip it if: nitrate in your test.

Pretreatment and upkeep on a well

• Hard or iron-bearing water fouls the membrane: Nebraska Extension says a softener ahead of RO can extend membrane life³, and Health Canada notes pretreatment may be needed⁵.
• No carbon prefilter on unchlorinated water? Nebraska Extension advises against activated carbon prefilters when the feed water is not chlorinated, because they can encourage microbial growth on the membrane³. Many units include one anyway; ask the maker.
• Cold water cuts output: 45 °F well water gives about half the output of 77 °F water³.
• Waste water. Estimates range from about 1 gallon wasted per gallon treated (EPA)¹³ to 2.3 to 4 gallons (Nebraska Extension, 20–30% recovery)³. The EPA’s WaterSense label requires at least 30% efficiency¹⁴. On a septic system, that water adds to the load³.
• Filters and membrane. Penn State gives about 6 to 12 months for carbon blocks and 12 to 24 months for RO cartridges¹⁵. Health Canada advises periodic lab tests of the water going in and coming out⁵.