The LS3-Custom-20GPM Emergency Fresh Water Purification Unit provides the equipment operator with the means to produce large volumes of potable water at a low cost and a minimum of logistics planning. It is incumbent upon the LS3-Custom-20GPM operator to carefully analyze the ambient water supply and make adjustments during the various treatment phases, i.e., pre-filtration, rate of flow, chlorine injection, retention time, ultraviolet exposure and sanitary storage. When operated in conformity with the basic operation manual, the LS3-Custom-20GPM Fresh Water Purification system can produce drinkable water up to 1200 gallons an hour with the high degree of purity to meet standards developed by USEPA, WHO and European Directives for producing potable healthful water.