Reverse Osmosis for Madison Drinking Water
RO earns its place at the kitchen sink in a softened Madison house. Whole-home RO is a much bigger decision, and it's rarely needed here.
Under-sink reverse osmosis costs about $200–$800 for the unit plus $100–$1,000 to install; whole-home RO runs $3,000–$10,000 installed (HomeBuddy, 2026). In Madison, RO at the kitchen sink is the usual partner to a softener: it removes most of the sodium softening adds, plus most dissolved minerals and many trace contaminants.
Sodium: from the softener and from some wells
Ion exchange swaps hardness minerals for sodium, and very hard water means more of the swap. Some Madison wells also carry sodium before any softener touches it. Well 14 measured 66 mg/L in 2025, above an EPA guideline of 20 mg/L meant for people on sodium-restricted diets, and the utility links rising sodium at several wells to road salt (Madison Water Utility). RO removes most sodium at the one faucet you drink from.
Older plumbing and other reasons people choose RO
The utility has removed every known lead service line, but lead solder was used in home plumbing until 1986, and lead water pipes were commonly installed in Madison homes until 1929 (Madison Water Utility 2025 report). The utility's report says a filter approved by an ANSI-accredited certifier to reduce lead is effective at cutting exposure. Many RO systems carry that listing; check the performance sheet. RO also cuts PFAS and nitrate, both found at low levels in several wells in 2025.
Under-sink versus whole-home
Under-sink systems use sediment and carbon pre-filters, a membrane, a small storage tank and a dedicated faucet, with an optional line to the fridge. Whole-home RO treats every drop, needs a storage tank and repressurizing pump, and sends a steady stream to the drain. On municipal Madison water that meets standards, it's hard to justify. Prices sit side by side on the Madison softener and RO price guide.
Upkeep you should budget for
RO isn't install-and-forget. Sediment and carbon pre-filters protect the membrane and need changing on the maker's schedule, and the membrane itself wears out after some years of use. HomeBuddy's 2026 guide puts filter and membrane replacements at about $100 to $300 a year. On very hard, unsoftened Madison water, membranes scale faster, which is one more reason RO usually sits after the softener rather than in place of it.
Questions homeowners ask
Should RO go before or after the softener?
After. Softened water is easier on the membrane, and RO then removes most of the sodium the softener added, so the kitchen faucet gets the lowest-mineral water in the house.
Does RO waste water?
Every RO system sends some water to the drain. Newer designs waste far less than older ones, so compare the stated ratio of drain water to filtered water before you buy.
Find out what your Madison well delivers
Tell us what you're noticing: crusty faucets, a tired softener, brown water now and then, or a question about PFAS. A local water treatment specialist serving Madison calls you back.