· Michael Blair
Reverse osmosis pushes water through a membrane that rejects almost everything dissolved in it. That makes it the most complete household treatment, and it has real trade-offs.
What it removes
Dissolved solids broadly — lead, nitrates, fluoride, sodium, and most contaminants of concern. It is the standard answer where a test has found something specific that carbon does not address.
It is generally paired with pre- and post-carbon stages for chlorine and taste.
The trade-offs
It produces slowly, which is why systems have a storage tank, and it sends several litres to drain for each litre produced. It also removes beneficial minerals, which some systems add back.
Water treated by reverse osmosis is slightly acidic and aggressive, which is why it should not be plumbed into a whole-house system in older pipework.
- Removes dissolved solids broadly, including lead
- Produces slowly and needs a storage tank
- Sends several litres to drain per litre produced
- Removes minerals; some systems remineralise
- Membrane lasts years, pre-filters need regular changes
When it is the right choice
When a test of your own tap has found something specific — lead from household plumbing, nitrates, or high dissolved solids — that carbon filtration does not address.
Buying it without a test is common and frequently unnecessary, since a good carbon block handles chlorine taste for far less.
Maintenance
Pre-filters protect the membrane and need changing on schedule, typically every six to twelve months. The membrane itself lasts years if the pre-filters are maintained and fails early if they are not.
Sanitise the system and the tank when changing the membrane.