Semipermeable membrane filtration
How a Reverse Osmosis works
Pushes water through a fine membrane that removes the dissolved solids most filters miss.
Typical cost: $300–$1,000 installed
How it works
Reverse osmosis (RO) forces water under pressure through a semipermeable membrane with openings so small that dissolved salts, metals, and many chemicals can't pass through.
Clean water collects on the other side and fills a small storage tank; the rejected contaminants are rinsed down the drain. Most home RO units are installed under the kitchen sink for drinking and cooking water.
Pre-filters protect the membrane from sediment and chlorine, and a final carbon polish improves taste right before the water reaches your faucet (NSF/ANSI 58).
The components inside
What each part does, in the order water moves through the system.
- 1Sediment pre-filterCatches grit and rust so they don't clog the membrane.
- 2Carbon pre-filterStrips chlorine, which would otherwise damage the membrane.
- 3RO membraneThe heart of the system — removes dissolved solids and metals.
- 4Storage tankHolds purified water so you get flow on demand.
- 5Post-carbon filterFinal polish that perfects taste at the faucet.
What it addresses
- Dissolved solids, lead, arsenic, chromium-6, nitrate, fluoride
- PFAS, copper, and many other dissolved contaminants
- Off-tastes and odors from the drinking-water tap
Learn about these contaminants
Pros & cons
Pros
- The broadest at-the-tap removal of dissolved contaminants
- Dramatically improves taste of drinking and cooking water
- Compact, under-sink — no whole-home plumbing changes
Cons
- Sends several gallons to the drain for each gallon produced
- Slower flow; relies on a small storage tank
- Removes beneficial minerals too — some units re-mineralize
Best for
Anyone who wants the cleanest possible drinking and cooking water at one tap.
Sizing basics
- Rated by gallons-per-day membrane output (50–100 GPD covers most homes).
- Storage tank size sets how much purified water is ready at once.
- Filters are swapped every 6–12 months; the membrane lasts 2–5 years.
Solves these water problems
Next steps
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Sources
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Advertising disclosure
The Very Good Water Company is an authorized WaterTech dealer and earns revenue from installations and lead referrals.