How Does a Reverse Osmosis System Work?

Reverse osmosis forces water through a membrane so fine that most dissolved substances can't follow it. What comes out the other side is some of the cleanest drinking water you can get at home. What gets left behind goes down the drain.

That's the whole idea. Now here's what's actually happening in the cabinet under your sink.

An RO system isn't just the membrane — it's a sequence of filters, each doing a specific job before the water reaches the membrane and after it comes out:

• Sediment pre-filter: catches sand, rust, and particles so they don't clog the membrane
• Carbon pre-filter(s): reduce chlorine and organic compounds that would damage the membrane
• The RO membrane: the heart of the system — rejects dissolved contaminants down to the molecular level
• Carbon polishing filter: removes any remaining taste and odor right before the tap
• Storage tank: holds your filtered drinking water so it's ready when you want it

Some systems add a remineralization stage that puts calcium and magnesium back into the finished water. RO strips almost everything out — which is great for purity but can leave water tasting flat. Remineralization restores a clean, balanced taste.

The membrane is a sheet of material with pores measured in microns — small enough that water molecules can pass but most dissolved solids, including many minerals, chemicals, and metals, can't. Water pressure pushes the clean water through; the contaminants stay on the other side and are flushed out as waste.

That's why RO water tastes different. You're not just filtering out the chlorine taste — you're reducing a broad range of things you can't taste, smell, or see.

Curious whether RO makes sense for your home? See our reverse osmosis systems page.