Water purification
Distillation

Distillation involves boiling water to produce water vapour. The vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vaporised, they remain in the boiling solution. Even distillation does not completely purify water, because of contaminants with similar boiling points and droplets of unvapourised liquid carried with the steam. However, 99.9% pure water can be obtained by distillation.

Direct contact membrane distillation (DCMD) passes heated seawater along the surface of a hydrophobic polymer membrane. Evaporated water passes from the hot side through pores in the membrane forming a stream of cold pure water on the other side. The difference in vapour pressure between the hot and cold side helps to push water molecules through.
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