Under-sink reverse osmosis, explained simply.

What is an under-sink RO system?

Reverse osmosis (RO) is a filtering method that pushes water through a very fine membrane. An under-sink RO system fits in the cabinet below your kitchen sink and sends filtered water to its own small faucet on the counter.

Most systems also use several filter stages before and after the membrane. Together they work on your tap water to improve how it tastes and looks.

Who is it for?

• Households that drink or cook with a lot of tap water and want it to taste better.
• People who buy bottled water regularly and want a simpler option.
• Renters and homeowners who want a system that fits under a standard sink without a big project.

What to look for

Tankless or tank

Tankless systems are compact and filter water on demand, so they free up cabinet space. Tank systems store filtered water, which can help if your cabinet has room and you like a steady reserve.

Flow rate

Flow rate tells you how quickly filtered water comes out. A higher flow rate means less waiting when you fill a pot or a large bottle.

Filter life

Every filter has a replacement schedule. Longer-lasting filters mean fewer changes, but always follow the maker's guidance for your system.

Installation

Look for clear instructions, quick-connect fittings, and a size that fits your cabinet. Many people install a system themselves in an afternoon. A plumber can help if you prefer.

Water use and drain

RO systems send some water to the drain as part of filtering. Check how much a system uses, and whether your sink setup can handle the drain connection.