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. The object of water treatment is to provide potable water, i.e. pathogen free and chemically safe, which is low in physical impurities and is also aesthetically acceptable to the consumer. However the greatest health risks in the overwhelming majority of situations where disasters occur are due to the presence of pathogens (microbiological contamination), where as chemical contamination is rarely on immediate health impact. Therefore these guidelines reflect this and focus accordingly. However it maybe that in the future that greater risks will be presented by chemical pollution of water and for example the extensive arsenic poisoning of groundwater in Bangladesh and Eastern India highlights that there can be other longer term detrimental health impacts.