How much is a reverse osmosis water system depends far less on the brand than on four decisions: whether it treats one tap or the whole house, whether it uses a storage tank or a pump, whether you fit it or an installer does, and what the replacement cartridges and membrane will cost you every year afterward. The ongoing cost is the one buyers routinely leave out.
Point of use versus whole house
This is the largest single factor and it is a factor of many times, not a few percentage points. An under-sink system treats the kitchen tap with a small membrane at line pressure. A whole-house reverse osmosis system needs a large membrane array, a pressurized storage tank, a repressurization pump, pre-treatment to protect the membrane, and often remineralization afterward to stop the water attacking the plumbing. They are different classes of equipment aimed at different problems.
How the unit is built
Within under-sink systems, the price ladder runs from basic cartridge-and-tank units with standard housings, through quick-change cartridge designs that trade cartridge cost for easier maintenance, to tankless designs with a booster pump that produce on demand and free up the cabinet. More stages is not automatically better. Certified performance for the contaminants you actually have is worth paying for, and extra unnecessary stages are just extra cartridges to buy.
Installation and the awkward extras
A straightforward under-sink install into an existing cabinet with an accessible angle stop and a spare faucet hole is a short job. What adds to it is drilling a stone or composite countertop for the faucet, running a line to a refrigerator, adding a booster pump and an outlet where feed pressure is low, or a drain connection that is not simple to reach. Well systems frequently need the pump, so include it in the quote rather than discovering it at commissioning.
The running cost nobody quotes
Sediment and carbon pre-filters are changed roughly annually, the membrane lasts several years if the pre-filters are kept up, and a polishing cartridge goes at the same time as the pre-filters. Neglecting the pre-filters is what turns a long-life membrane into an annual purchase. Some water goes to drain as concentrate, which shows on the water bill in metered areas. Our reverse osmosis cost guide sets out the verified vendor prices in the table there, drawn from the manufacturers' own published pages.
Questions people ask about how much is a reverse osmosis water system
Is a whole-house reverse osmosis system much more expensive?
Substantially, and not by a small margin. It needs a large membrane array, storage, a repressurization pump and pre-treatment, so it is a different class of equipment entirely.
Do more filtration stages mean a better system?
Not necessarily. Certified performance against the contaminants you actually have matters more, and every extra stage is another cartridge to buy on schedule.
What does an RO system cost to run each year?
Pre-filters annually, a membrane every few years if the pre-filters are maintained, plus the water sent to drain as concentrate on a metered supply.
Can I install an under-sink RO system myself?
Many homeowners do, if the cabinet has an accessible cold angle stop, a drain connection and a spare faucet hole. Drilling stone countertops is the job to hand over.