In this guide
Reverse osmosis (RO) uses pressure to push water through a semi-permeable membrane, leaving dissolved contaminants behind and sending them down the drain. It's one of the most thorough ways to purify drinking water at home.
The stages of reverse osmosis
- 1Pre-filtration
Sediment and carbon filters remove particles and chlorine that would damage the membrane.
- 2RO membrane
Water is forced through the membrane, which holds back dissolved salts, metals and other contaminants.
- 3Post-filtration
A carbon post-filter polishes the taste before the water reaches your faucet.
What is an RO membrane?
A semi-permeable membrane is a thin layer that lets water molecules through but blocks larger molecules and ions. In an RO system, it separates clean water from dissolved salts, metals and microorganisms.
What does reverse osmosis remove?
RO removes most dissolved contaminants, including sodium, chloride, copper and lead, and reduces arsenic, fluoride, sulphate, nitrate, calcium and magnesium. The membrane also blocks bacteria and viruses, though for untreated well water we still recommend UV disinfection.
Types of RO systems
All RO systems use a membrane; the difference is in the filters around it and how the water is stored.
- 4-stage RO: sediment filter, carbon filter, membrane and post-carbon filter
- 5-stage RO: adds a storage tank for bigger households, plus an optional alkaline cartridge
- Tankless RO: high flow with no tank and less waste, like the Big Flow RO
Where can you install an RO system?
- Under the kitchen sink: the most common spot, with its own faucet
- Countertop or inside a cabinet: for rentals and condos
- To a fridge or ice maker: for clean water and ice
- On a private well: for safe drinking water (with UV)
- In an office, RV or cottage: anywhere you want clean drinking water
Whole-home RO is possible, but nine times out of ten it's unnecessary. A drinking-water system plus a whole-home filter or softener is far more cost-effective.
How is RO different from a regular filter?
A carbon filter removes chlorine, taste and odour; RO also removes dissolved solids that carbon can't touch, such as salts, lead and fluoride. RO does send some water down the drain as it works.
What maintenance does RO need?
Change the pre- and post-filters about once a year, sanitize the system yearly, and replace the membrane every 2 to 3 years. Compare our reverse osmosis systems.
