Health Hygiene & Sanitation

Lesson 26 : Water Purification

Filtration

Supernatant Water

The water above sand bed is called supernatant water. The depth varies from 1 to 1.5 metre. The purposes of supernatant water are:

• To provide constant head of water so that resistance of the filter can be overcome and downward flow of water can be promoted;


• To provide waiting period (3 to 12 hours) for raw water to undergo partial purification by sedimentation, oxidation and particle agglomeration.

The level of supernatant water is always kept constant.