Reverse Osmosis Water Filters: Complete Guide
How RO systems work, when you need one, and what to look for.
How reverse osmosis works
Water is forced through a semipermeable membrane with pores small enough to block dissolved solids, minerals, PFAS, lead, arsenic, and most contaminants. The rejected contaminants are flushed to drain. RO typically removes 95-99% of dissolved solids.
When you need RO
PFAS contamination above EPA limits, high TDS (500+ PPM), arsenic, or fluoride are the primary reasons for RO. For hard water alone, a softener is more appropriate and less wasteful. RO wastes 2-4 gallons for every gallon produced.
Point-of-use vs. whole-house
Under-sink RO systems ($150-400) treat drinking and cooking water only. Whole-house RO ($2,000-5,000+) is rarely needed and requires a pressure tank. For most households, an under-sink system paired with a whole-house softener covers all bases. See our decision guide.