On the Westside, reverse osmosis is the most common recommendation we make, because it fits almost every home: houses, condos and apartments. It sits under the kitchen sink and makes the water you drink and cook with.
It is also the system people understand least. Here is what happens inside one, what it removes and does not, and what it takes to keep it running.
What does reverse osmosis remove?
Most dissolved solids, including calcium, magnesium and sodium, plus the disinfectant taste through its carbon stages. It produces purified water for drinking and cooking at one faucet.
The membrane is what makes RO different from a regular filter. Its openings are small enough to hold back most dissolved minerals, which is why RO water tastes clean and leaves no film in a kettle, even in very hard water areas like Culver City and Inglewood.
Chloramine is the exception that matters on the Westside. The Water Quality Association lists it among the things that are difficult to remove by RO alone, so the carbon stage ahead of the membrane does that work. A system with a weak carbon stage can still let the pool taste through.
What does each stage of an RO system do?
Sediment and carbon stages protect the membrane and remove taste, the membrane removes dissolved solids, and a final carbon stage polishes the taste on the way to the faucet.
| Stage | What it does | Typical change interval |
|---|---|---|
| Sediment pre-filter | Catches sand, rust and particles that would clog the membrane | Roughly yearly |
| Carbon pre-filter | Removes chlorine and chloramine, which protects the membrane and fixes taste | Roughly yearly |
| RO membrane | Removes most dissolved solids, including hardness and sodium | Every few years |
| Post carbon filter | Polishes the taste of the water on its way to the faucet | Roughly yearly |
| Remineralization stage (some units) | Adds a small amount of minerals back for taste | Per the manufacturer |
Intervals vary with the unit and how much water you use. We give you the exact schedule for the system we install.
Systems are sold by stage count, but the count matters less than what each stage does.
How often do RO filters need to be changed?
The pre-filters and post-filter are typically changed about once a year, and the membrane lasts several years. Your water use and the unit's design set the exact schedule.
A household that drinks and cooks only with RO water uses its filters faster than one that fills a glass now and then. Many current units have an indicator that tells you when a filter is due. Changing the pre-filters on time also protects the membrane, which is the most expensive part.
What does an RO system cost to run each year?
The yearly cost is the replacement filter set, a share of the membrane's cost spread over its life, and the water the system sends to the drain. The exact dollar figure depends on the specific unit's filter prices.
We do not publish a single annual cost, because filter prices differ widely between brands and models, and a number that fits one unit would mislead you about another. When we quote a system, we give you the price of its filter set and the change schedule in writing, so you know the running cost before you buy.
Electricity is usually not a meaningful cost. Many tank systems run on water pressure alone, while some tankless units use a small pump and need an outlet under the sink, so check the spec sheet.
Does reverse osmosis waste water?
Yes, some. An RO system sends part of the water to the drain to carry away what the membrane rejects, and the ratio depends on the unit.
Newer units send less water to the drain than older designs. The manufacturer's spec sheet lists the ratio, and it is worth comparing when you choose a unit, along with filter prices.
What should you look for when choosing an RO system?
Certification to NSF/ANSI 58, the standard for reverse osmosis systems, a carbon stage suited to chloramine, filters you can buy easily, and a size that fits your cabinet.
NSF/ANSI 58 certification means the system's performance claims were tested against the reverse osmosis standard, so look for it on the product listing rather than taking a stage count on faith.
On the Westside, the carbon stage matters as much as the membrane, because most utilities here use chloramine. Ask what the carbon stage is rated for. Then check the practical things: whether replacement filters are a common size or a proprietary cartridge, what the unit sends to the drain, and whether a tank fits under your sink or a tankless unit makes more sense.
Can you install RO in a condo or apartment?
Yes. An under-sink RO system needs only a cold water line, a drain connection and a faucet hole, and a countertop RO unit needs no installation at all.
That is why RO is the starting point in Marina del Rey and for many units in Santa Monica and Venice. Our condo and apartment guide covers what needs landlord or HOA approval.
Want purified drinking water at your kitchen sink? Pipe Dream Plumbing Co. installs under-sink reverse osmosis in Westside houses, condos and apartments. Call (310) 957-1763.