Changes

[[Image:presettle icon.png|right|100px]]

[[Image:storage and sedimentation.jpg|thumb|right|300px|Storage and sedimentation. Drawing: WHO.]]

The quality of raw water can be improved considerably by storage. During storage, non-colloidal, suspended particles slowly settle to the bottom of a storage tank, and solar radiation will kill some of the harmful organisms in the water. Schistosoma larvae, for example, will die after storage for at least 48 hours. In contrast, colloidal particles remain in suspension. The smaller the suspended particles, the longer the water needs to be retained in the reservoir. If the suspended matter precipitates very slowly, chemicals can be added to induce coagulation and flocculation.