Reverse Osmosis
Reverse osmosis is one of the most thorough point-of-use treatment options, typically installed under the kitchen sink.
Short answer: RO systems push water through a semi-permeable membrane, removing a broad range of dissolved contaminants when properly certified and maintained. They're point-of-use (usually one tap), not whole-house, and require periodic membrane and filter changes.
What RO can address
- A broad range of dissolved solids and contaminants, depending on certification
- Nitrate, arsenic, and PFAS when the specific system is certified for them
- Improved taste from reduced dissolved solids
What to know before buying
- Confirm NSF/ANSI certification for the specific contaminant you're addressing — certification is claim-specific, not universal.
- RO systems produce wastewater; check the system's efficiency ratio if that matters to you.
- A storage tank buffers output since RO produces water slowly.
- Systems require periodic pre-filter, membrane, and post-filter replacement.
Common mistakes
- Assuming any RO system automatically removes every contaminant
- Skipping membrane replacement, which degrades performance over time
- Installing RO as a whole-house solution when it's designed for point-of-use
Official sources
- NSF/ANSI 58 (Reverse Osmosis Drinking Water Treatment Systems)
- U.S. EPA point-of-use treatment guidance
Related
Do I need RO if I already have a whole-house filter?
Possibly, if your whole-house filter isn't certified for a specific dissolved contaminant you're concerned about. The two serve different purposes and are often used together.
This page provides general educational information and does not endorse a specific manufacturer or product claim.
Last reviewed: 2026-07-11. Report a correction.