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Reverse Osmosis Systems for Well Water
Reverse osmosis systems for well water: under-sink tankless and tank-style units for drinking water, and whole house RO from 300 to 7,000 GPD for arsenic, nitrates, uranium, fluoride and high TDS at every tap. RO works on wells, but only on water that's been prepared for it: the guide below covers what a membrane can and can't take, the pre-treatment that goes ahead of it, and which system fits your test results. Free shipping, 5-year valve warranty on pre-treatment systems. Does RO remove iron, bacteria or nitrates? Answers below the products.
Reverse osmosis on well water: what works and what has to come first
Reverse osmosis is the only residential treatment that removes dissolved contaminants wholesale: arsenic, nitrates, uranium, fluoride, sodium, sulfates and high TDS all go, which is why it's the right answer when a well test comes back with something a filter or softener can't touch. The catch is that an RO membrane is a fine, expensive sheet of polymer that fouls on exactly the things wells are full of. Iron plugs it, hardness scales it, sediment blinds it, and bacteria grow on it. On a well, RO is the last stage of a treatment train, not the first.
What the membrane can take
| Feed water | Membrane limit | If you're over it |
|---|---|---|
| Iron (dissolved) | Under 0.3 ppm; under 0.1 for long membrane life | Iron filter ahead of the RO; a softener handles light iron |
| Manganese | Under 0.05 ppm | Katalox Light or Greensand iron/manganese filter |
| Hardness | Under 10 gpg for under-sink; soften for whole house | Well water softener; keeps the membrane from scaling and doubles its life |
| Hydrogen sulfide | None allowed; it fouls and smells through | Sulfur filter (air injection) |
| Sediment / turbidity | Under 1 NTU; 5-micron pre-filter minimum | Sediment filter; backwashing on sandy wells |
| pH | 6.5–8.5 | Acid neutralizer for low pH |
| Bacteria / coliform | RO blocks bacteria but isn't rated as disinfection and can grow biofilm | UV system ahead of (whole house) or after (under-sink) the RO |
| Pressure | 40 psi minimum for tank RO; tankless units have a pump | Check the pressure switch setting; a booster pump on low-pressure wells |
Get these numbers from a lab test before buying any RO for a well. Send us the report and we'll tell you what has to go in front of it, or whether a filter alone solves the problem without RO at all.
Under-sink or whole house?
Most well owners need RO for drinking and cooking only; the iron, hardness and odor problems that affect the whole house are solved by the filters and softener. An under-sink unit after that pre-treatment gives purified water at the kitchen tap for a few hundred dollars. Whole house RO is for wells where a dissolved contaminant has to be removed from every tap: arsenic above the limit, nitrates with infants in the home, uranium, radium, very high TDS or sodium from a softener you can't avoid. It needs a storage tank and repressurization pump and costs ten times as much.
| Under-sink RO | Whole house RO | |
|---|---|---|
| Treats | One faucet (plus fridge line on tank units) | Every tap, shower and appliance |
| Output | 75 GPD (tank) to 800 GPD (tankless) | 300–7,000 GPD into a 165–550 gal storage tank |
| Pre-treatment needed | Sediment and iron under the limits; softener recommended | Softener and iron filter required; UV after the tank |
| Best fit on a well | Nitrates, arsenic or TDS in drinking water; taste | Arsenic, uranium, radium or TDS that must be removed at every tap |
| Systems | Pentair GRO-575B · GRO-475M · GRO-475B (tank, no power) · Waterdrop G3P800 (tankless, UV) · G3P600 · G3 | Crystal Quest Whole House RO (300–7,000 GPD) · Commercial RO (500–7,000 GPD) |
| Price | $539–$1,005 | $2,744–$12,000+ |
On a well, the Pentair tank units have two advantages: they run on line pressure with no electronics, and their membranes are the standard 75 GPD type that tolerates variable feed water well. The Waterdrop tankless units are rated by Waterdrop for municipal water; after a softener and iron filter they run fine, and the G3P800's UVC-LED is a real plus on a well. See under sink reverse osmosis systems for the full comparison and whole house reverse osmosis systems for sizing.
The pre-treatment train, Clack and Fleck side by side
From the pressure tank toward the RO: sediment, then iron or sulfur, then softener, then (for whole house) UV. The RO goes last.
| Stage | Clack | Fleck |
|---|---|---|
| Iron + sulfur (air injection) | C-Series AIO (from $1,999) | 5600 SXT AIO Iron (from $1,319) · 5600 AIO Sulfur (from $1,539) |
| Iron + manganese (Katalox Light) | Katalox Light Filter (from $1,279) | 2510 AiQ Katalox Light (from $1,759) |
| Hardness (softener) | WS1 Water Softener (from $1,319) | 5600 SXT Water Softener (from $879) |
| Sediment / low pH | Backwash Sediment · Acid Neutralizer | — |
| Bacteria (UV) | VIQUA UV systems; sized to the house flow for whole house, or a tap-size unit after an under-sink RO | |
What RO removes from well water, and what it doesn't
Does reverse osmosis remove bacteria? The membrane physically blocks bacteria, viruses and cysts, but RO systems aren't certified as disinfection: seals leak, and bacteria colonize the membrane and the storage tank. If a well tests positive for coliform, treat it with UV; RO alone isn't the fix.
Does reverse osmosis remove nitrates? Yes, typically 85–95%, and it's the standard residential method. Nitrates matter most for infants and pregnancy; an under-sink RO on the kitchen tap covers drinking and formula water.
Does reverse osmosis remove arsenic? Arsenic V, yes, 90%+. Arsenic III (common in reducing groundwater) passes through more easily and is oxidized first, which an iron filter with air injection or chlorination does as a side effect. Dedicated arsenic filters are the alternative for whole-house removal without RO.
Does reverse osmosis remove iron? It will, but it shouldn't be asked to. Iron above a trace fouls the membrane in weeks. Remove it ahead of the RO with an iron filter or softener.
Reverse osmosis vs water softener on a well? They do different jobs. The softener removes hardness (and light iron) from all the water in the house and protects the RO; the RO removes dissolved contaminants from drinking water. Most wells that need RO need the softener too, in that order.
Can you use reverse osmosis with well water at all? Yes, once iron, hardness, sediment and sulfur are under the limits in the table above. Skip the pre-treatment and you'll replace membranes every few months and wonder why RO "doesn't work on wells".
Not sure what your well needs? Call 800-374-2143 or send your water test. Related: well water filtration systems · nitrate filters · arsenic filters · coliform treatment · all reverse osmosis systems.
