In West Pakistan the water lost by evaporation from a square mile of the free water surface area is about 5 cusecs. Oily and fatty films when spread on water surface reduce the evaporation. Fatty alcohols having higher molecular weight are best suited as monolayers. Cetyl alcohol and stearyl alcohol give the best results. Different methods of treatment with chemical compounds are described with figures. Cotton seed oil and its derivatives may also be used. Detection of monolayers may be carried out by using camphor crystals. Three maps of West Pakistan showing evaporation contours and two tables indicating evaporation losses are provided. Different evaporation retardents with their evaporation saving percentages are also tabulated.