A small system for one tap, under the sink.
Reverse osmosis sits in the cabinet under your kitchen sink and feeds a dedicated faucet. It is the small job. No main line, no tank in the garage.
How reverse osmosis works
Household pressure pushes water against a very fine semipermeable membrane. Some water passes through to a small storage tank. The rest carries what didn't pass to the drain. That's normal for the process, and the ratio varies by model.
Because a membrane works slowly, most under-sink systems store a small amount and send it to a separate faucet on the counter. So you keep your regular faucet for dishes and use the small one for a glass or a pot.
The stages in a typical unit
- 1
Pre-filters
One or more cartridges up front, usually a sediment stage and a carbon stage, to protect the membrane behind them.
- 2
Membrane
The heart of the system. A wrapped sheet of semipermeable material in a small housing.
- 3
Storage tank
A small pressurized tank, so water is ready at the faucet. Some newer designs skip the tank and use a pump.
- 4
Post-filter and faucet
A last small cartridge on many models, then a dedicated faucet that mounts at the sink.
It usually makes sense when
- You mainly care about what you drink and cook with.
- You're in a condo or townhome and the main line isn't yours to touch.
- You have room in the sink cabinet, with the disposal and trash pull-out accounted for.
It may not be the right call when
- You want the same water at the shower. It only serves the faucet it's connected to.
- The cabinet is full and you won't give up the space.
- Your countertop can't take a faucet hole and there's no open spot in the sink deck.
What we look at in your photos
- Cabinet width, depth and what's already in there
- Shutoff valve condition under the sink
- Drain arrangement, and whether a disposal is on it
- An open hole in the sink deck, or the countertop material if not
What upkeep looks like
- Pre and post-filters. These are the regular replacements, and they're quick swaps on most models. [interval pending supplier spec]
- Membrane. Replaced less often than the filters around it. How often depends on the model and your water. [interval pending supplier spec]
- Tank. If you have one, tanks can lose their air charge over time. It shows up as slow flow at the faucet.
The lineup comes with real numbers, or not at all.
| Model | [model and brand pending supplier] |
|---|---|
| Installed price | [price pending supplier] |
| Independent listing | [certification listing pending supplier] |
| Warranty | [warranty terms pending supplier and counsel] |
| Standard install scope | [standard install scope pending plumber review] |
Common questions
Why is there a separate faucet?
A membrane makes water slowly, so it can't keep up with a full-flow kitchen faucet. The small faucet is what lets it work from stored water.
Does it waste water?
Some water goes to the drain by design. The ratio depends on the model, the membrane and your water pressure. We'll give you the number for the specific model on your written price once the lineup is set.
Can it connect to my fridge?
Often yes, with an extra line, if the fridge is close enough to route it. Tell us on the call and send a photo of the path, because it changes the install scope.
Will it fit with my garbage disposal?
Usually, but disposals take up space and change where the drain connection can go. That's exactly why we ask for the cabinet photo first.
