Best Under-Sink Water Filters for 2026: RO and Filter Systems

A carbon filter improves taste and removes chlorine and some contaminants. Reverse osmosis removes dissolved solids too, including the things a carbon filter cannot - at the cost of waste water and a slower flow.

Tankless versus tank

Tankless RO saves the space under the sink and avoids the tank going stale, but you pay more upfront. Tank systems are cheaper and slower.

The number that matters: waste ratio

Older RO systems waste three or four litres for every litre produced. Modern tankless units are far better - check the ratio, not just the claim of 'efficient'.

Filter cost per year

A cheap system with expensive cartridges is not cheap. Multiply the cartridge price by how many you replace per year before deciding.

Installation reality

Most inline filters are a ten-minute DIY job. RO units need a drain connection and a hole in the counter for the tap, which is a bigger commitment.

FAQ

RO or carbon filter?

Carbon for taste and chlorine; reverse osmosis if you want dissolved solids and heavy metals reduced as well.

Do I need a plumber?

For an inline filter, usually not. For a tankless RO with a dedicated tap, most people prefer a plumber.

How often do filters need replacing?

Typically six to twelve months for carbon stages, one to three years for an RO membrane.

Does RO remove healthy minerals?

It removes most dissolved minerals. Some units add a remineralisation stage if that matters to you.

Are the links on this page affiliate links?

Some are. If you buy through them we may earn a commission, and it never changes a ranking.

Conclusion

For most kitchens the tankless RO system is the best long-term buy: it removes the widest range of contaminants, wastes far less water than older designs, and saves counter space. If you only want better-tasting water and simple installation, an inline under-sink filter does that for a fraction of the price and a ten-minute install.