This manual is part of a series of guides devised by the Oxfam Public Health Engineering Team to help provide a reliable water supply for populations affected by conflict or natural disaster. Storage tanks are required for collection of water from springs or water produced from continuous flow water treatment systems, e.g. from upflow clarifiers or slow sand filters. There should be sufficient storage volume to store all water produced overnight, as this is unlikely to be collected by users during the night. Storage tanks also have secondary functions such as ensuring a constant water supply to treatment processes, providing a level of treatment by settlement of larger suspended solids and maintaining pressure in distribution systems