The evaporation rate of Algerian arid zones open water bodies is extremely large and reaches 3.8 m per year. To minimize these losses in water reservoirs monolayers of Hexadecanol are used. To check the efficiency of Hexadecanol monolayer and determine the adequate quantity of substance to use, a comparison was performed between the evaporation rate of water across two kinds of interfaces, namely an air/water interface and an air/monolayer/water interface (using Hexadecanol monolayer). Trials were conducted under natural conditions by using three tanks of one meter square surface which were partially buried. The first tank surface was covered by Hexadecanol at a concentration of 0.09 g/m2, the second by Hexadecanol at a concentration of 0.15 g/m2; and the third (the ‘control’) contained only water. Both monolayer treatments were applied to the respective water surface every three days. Daily observations spanning one month showed that films reduced the losses by evaporation and the rates of the evaporation reduction are significant (19% in the first tank and 24% in the second tank). Analysis with respect to prevailing meteorological conditions is presented and implications for the use of Hexadecanol in the Algerian arid zone are discussed.