Reverse osmosis for well water: when you need it and where it goes
Short answer
Reverse osmosis (RO) is the strongest drinking-water treatment for arsenic, nitrate, PFAS and dissolved salts. On a well it belongs at the kitchen tap, after whole-house treatment for sediment, iron and hardness. Those foul the membrane quickly. Look for certification to NSF/ANSI 58 for the specific contaminants on your test.
What RO handles on a well
| Contaminant | RO at the tap? | Notes |
|---|---|---|
| Arsenic | Yes | Best on arsenic V; check certification |
| Nitrate | Yes | Check certification for nitrate |
| PFAS | Yes | EPA set 4 parts per trillion limits for PFOA and PFOS in public water |
| Iron, manganese, hardness | No | Treat at the whole-house level first |
| Bacteria | Not as the only barrier | Use UV or chlorination for bacteria |
Whole-house RO?
It exists, but it's expensive, wastes a lot of water and needs storage and repressurizing. For most homes, whole-house treatment plus RO at the kitchen tap covers drinking water at a fraction of the cost.
Questions well owners ask
Do I need reverse osmosis for well water?
Only if your test shows something RO is best at: arsenic, nitrate, PFAS or high total dissolved solids. Iron, sulfur and hardness need other systems.