If you've been reading about water quality in Connecticut, you've probably run into reverse osmosis. It comes up in almost every discussion of PFAS in Fairfield County, lead in Waterbury and Bridgeport, nitrates in the River Valley, and arsenic and uranium in eastern CT. There's a reason for that. It works.
But "it works" covers a lot of ground. The details matter before you spend $300 to $800 on a system.
What Does Reverse Osmosis Actually Remove from Water?
Reverse osmosis forces water through a semi-permeable membrane under pressure. Systems certified to NSF/ANSI Standard 58 have been independently tested to verify performance. The membrane's pores are small enough to block dissolved solids (ions, molecules, and particles) while letting water molecules pass. What comes out the other side has far less dissolved contaminant in it.
What RO removes effectively (to 95%+ reduction):
- PFAS (all major compounds)
- Lead
- Arsenic
- Nitrates
- Uranium
- Chromium-6
- Fluoride
- Most dissolved heavy metals
- Dissolved salts (including sodium from water softeners)
What RO does not remove effectively:
- Chlorine and chloramine (the carbon pre-filter stage removes these, not the membrane itself)
- Some volatile organic compounds (VOCs), which require a carbon stage
- Dissolved gases like radon (radon requires aeration, not filtration)
The Water Waste Issue
RO systems produce a "reject stream," the water that carries concentrated contaminants away from the membrane and down the drain. For every gallon of treated water produced, a typical residential RO system sends 3 to 4 gallons down the drain.
For a Connecticut household that uses 50 gallons of drinking and cooking water per day, that's 150 to 200 gallons of water wasted daily. At Connecticut water rates, the waste adds roughly $15 to $25 per month to your water bill.
Higher-efficiency RO systems (sometimes called "permeate pump" systems) can cut the waste ratio to 1:1 or better. They cost more upfront but pay back in reduced water waste.
The Maintenance Reality
An RO system requires regular maintenance:
- Pre-filter replacement: every 6 to 12 months
- RO membrane replacement: every 2 to 3 years
- Post-filter replacement: every 12 months
- UV bulb replacement (if included): annually
Skip the maintenance and the system stops doing its job. A membrane that hasn't been replaced in five years may not be removing PFAS to the levels it did when new. If you install an RO system, build the maintenance schedule into your calendar.
Which Connecticut Homeowners Need Reverse Osmosis?
For Fairfield County homeowners on Aquarion's system with PFAS concerns: an under-sink RO system at the kitchen tap is the most effective immediate action you can take.
For Waterbury and Bridgeport homeowners with lead concerns: an NSF/ANSI 53 certified carbon filter is enough for lead reduction, and it costs less than RO. RO is not necessary for lead alone.
For eastern CT well owners with nitrate or arsenic concerns: RO is the most effective treatment for both.
For Litchfield County well owners with radon concerns: RO does not remove radon. The CT DPH identifies aeration as the only effective method at or above 10,000 pCi/L for radon in water.
The right filter depends on what's in your water. The only way to know what's in your water is to test it. If you're not sure where to start, our guide on how to read your water quality report walks you through what the numbers mean.
Want ZIP-level context before deciding whether to test? Enter your ZIP code at CheckYourTap.com to see available public-system or regional monitoring records associated with the ZIP. This is not a test of a tap, well, or property. Free, in 30 seconds.
Keep Reading
- Boiling Your Water Removes Some Things and Concentrates Others. Know the Difference Before You Boil.
- The Chemical Your Water Utility Uses to Keep You Safe Is Creating New Problems in the Process
- Your Water Quality Report Arrived. Here's How to Actually Read It.
- The Water Test Your Bank Required Doesn't Test for What's Actually Dangerous
Sources: NSF International RO Certification Standards; EPA Drinking Water Treatment Technologies; WQA (Water Quality Association) RO Performance Data; CT DPH Water Treatment Guidance.
