Drinking Water Treatment

Introduction These guidelines are partly based upon the use of Oxfam equipment packages, which are devised by the Oxfam Public Health Engineering Team to help provide a reliable water supply where mass displacement of people has occurred, e.g. as found in refugee camps and relief centres. Work with smaller communities who may not have been displaced from their homes, requires the use of different treatment approaches, although often using the same basic treatment methods. Equipment and approaches appropriate for these situations are also included. The techniques and equipment described here reflect the most current practice of Oxfam GB humanitarian department. However a programme of ongoing applied research and development means that some of these approaches will be improved and modified in the future and these will be incorporated into subsequent revisions of these guidelines. Thus these guidelines serve in part to indicate future possibilities as well as describe what is currently possible. 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. In the early stages of water supply in an emergency, water quality (and quantity) may well fall below WHO recommendations, in which case the initial emphasis will be on raising both quality (and quantity) to come within acceptable limits in the shortest possible time. It is also desirable in emergency situations to provide an extra level of protection in the water, in the form of a chlorine residual, to deal with contamination at a household level, e.g. in water containers. Surface water sources often present the quickest option for water supply in the short term, but surface waters, unlike most ground waters, are much more prone to contamination by suspended solids and pathogens. This in turn often means that the biggest treatment problems encountered are the removal of suspended solids and providing means of effective disinfection. In choosing a water source(s), the quality of raw water has to be balanced against the quantity available. From a health point of view, a larger quantity of relatively good quality water is better than a small quantity of very high quality water and this must be taken into account by choosing sources that have sufficient quantity of water available. In some instances, where good quality water is limited, it may be necessary to provide two different qualities of water to consumers, reserving water from a poorer quality source for washing, whilst the water from a small good quality source could be used for food preparation and drinking. This may create difficulties in keeping the two water qualities separate, both for bulk production and at a household level and will also need considerable support from a public health promotion program if it is to be understood, acceptable and successful. Also one large source of dirty water, which though requiring more treatment than several small cleaner sources, may be more convenient from a management point of view, because all pumping/treatment systems could be centralised at one location. The selection of a water source depends not just upon its quality and quantity of water that needs to be supplied, but also its proximity to any proposed settlements, potential extraction difficulties and water rights, along with other issues. These guidelines will not go into these important factors that may influence the choice of a source, but rather concentrate solely upon treatment processes.