· by Michael Blair, Nashville's Water Filtration
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 does reverse osmosis remove?
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.
What are the downsides of reverse osmosis?
It produces slowly, which is why systems have a storage tank, and it sends several liters to drain for each liter 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 liters to drain per liter produced
- Removes minerals; some systems remineralize
- 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.
Sanitize the system and the tank when changing the membrane.
FAQ
What Reverse Osmosis Does and Does Not — questions
Does reverse osmosis waste water?
Yes — several liters go to drain for each liter produced, varying by system and pressure. Newer designs improve the ratio. For drinking and cooking volumes the absolute amount is modest, but it is one reason reverse osmosis is not used whole-house.
Does RO remove healthy minerals?
It removes dissolved minerals along with everything else, including calcium and magnesium. Whether that matters nutritionally is debated, since most mineral intake is dietary. Many systems include a remineralization stage, which also improves taste — water with nothing in it tastes flat to most people.
Do I need reverse osmosis or is carbon enough?
Carbon handles chlorine taste and odor, which is what most households actually object to, at far lower cost. Reverse osmosis is the answer when a test of your own tap has found something specific that carbon does not address. Test first — buying RO without one is common and often unnecessary.
How often should a reverse osmosis membrane be replaced?
The membrane lasts years when its pre-filters are kept up and fails early when they are not. Those pre-filters are there to protect it, and they typically need changing every six to twelve months. When the membrane itself is finally changed, sanitize the system and the storage tank at the same time.