- Unpressurised osmosis. The filtered water is deposited in a tank you can access. These are the fastest, most modern and safest units, and are therefore the best quality.
- Pressurised osmosis. The filtered water is deposited in a hermetically sealed tank: this makes them less secure and they also reject the most water (per litre of filtered water).
- Direct osmosis. As these have no tank, the filtered water comes out of the tap directly. They are slower and more expensive to maintain, as the parts do not last long.
