Reverse Osmosis for Well Water: Is It Right for You?
Reverse Osmosis for Well Water: Is It Right for You?
Reverse osmosis is the most effective point-of-use water treatment technology available. But it's not the right solution for every well water problem. Here's when RO makes sense — and when it doesn't.
How Reverse Osmosis Works
Reverse osmosis forces water through a semi-permeable membrane under pressure. The membrane has pores small enough to block dissolved salts, heavy metals, nitrates, bacteria, and most other contaminants — while allowing water molecules to pass through. The rejected contaminants are flushed down the drain.
A standard 5-stage under-sink RO system includes: a sediment pre-filter (removes particles), a carbon block pre-filter (removes chlorine and organics that damage the membrane), the RO membrane itself, a carbon post-filter (improves taste), and a storage tank that holds 2–4 gallons of treated water for immediate use.
RO systems produce water slowly — typically 50–100 gallons per day — which is why a storage tank is needed. The system runs continuously to keep the tank full.
What RO Removes (and What It Doesn't)
RO Removes (90–99%)
- Nitrates and nitrites
- Arsenic
- Lead
- Fluoride
- Dissolved salts (TDS)
- Bacteria and viruses
- Chromium
- Radium
- Copper (dissolved)
- Pesticides and herbicides
RO Does Not Remove
- Dissolved gases (hydrogen sulfide, radon)
- Some volatile organic compounds (VOCs)
- Chloramines (requires special membrane)
- Hardness (softener is more efficient for whole-home)
- Iron (pre-filter required to protect membrane)
When RO Is the Right Choice for Well Water
Nitrates above 5 mg/L
RO removes 90–96% of nitrates. This is the most important use case for well water RO — especially for households with infants under 6 months, for whom nitrates above 10 mg/L are dangerous.
Arsenic in the water
Arsenic is a known carcinogen with no taste or odor. RO removes 95%+ of arsenic. If your well tests positive for arsenic, RO is the most effective point-of-use treatment.
Lead in the water
Lead can enter well water from old plumbing, not just the well itself. RO removes 95%+ of lead.
High TDS (total dissolved solids)
If your water has a salty or mineral taste from high TDS, RO is the most effective treatment for improving drinking water taste.
Wanting the highest possible water quality for drinking and cooking
RO produces the purest drinking water of any residential treatment technology. Many homeowners install RO for peace of mind even when no specific contaminant is above the action level.
Critical: Pre-Treatment for Well Water RO
Well water requires pre-treatment before an RO system. Without it, the RO membrane will foul quickly and fail prematurely. Here's what's needed:
- Sediment pre-filter (5 micron minimum) — removes particles that clog the membrane
- Carbon block pre-filter — removes chlorine (from shock chlorination) and organics that degrade the membrane
- Iron pre-filter — if iron is above 0.5 ppm, an iron filter must be installed upstream of the RO system. Iron fouls the membrane rapidly.
- Acid neutralizer — if pH is below 6.5, the acidic water can damage the membrane over time
- Water softener — if hardness is above 10 GPG, scale can build up on the membrane. A softener upstream extends membrane life significantly.
Frequently Asked Questions
Does reverse osmosis remove nitrates from well water?
Yes — a properly functioning RO membrane removes 90–96% of nitrates. This is one of the primary reasons to install RO for well water, especially for households with infants under 6 months.
Do I need a pre-filter before a reverse osmosis system?
Yes — for well water, pre-filtration is essential. High iron, sediment, or chlorine will foul the RO membrane quickly. A sediment pre-filter and carbon pre-filter are required. If iron is above 0.5 ppm, an iron filter should be installed upstream of the RO system.
How much does a reverse osmosis system cost?
A point-of-use under-sink RO system typically costs $400–$800 installed. A whole-home RO system costs $2,000–$5,000+. For most households, a point-of-use system for drinking and cooking water is the most cost-effective approach.