Pushing water through a semi permeable membrane using external pressure is known as reverse osmosis.
Most water impurities do not pass through the membrane, which has a molecular weight cut off in the 300 Dalton range.
The impurities collect on the membrane surface and are flushed to the drain.
A popular pre-treatment before distillation, or deionazation systems, reverse osmosis can also be used to purify water for general use such as glass and plasticware washing.
Primer: Lab Water Purification Technologies