Abstract: The extremely high rate of evaporation from water surfaces in arid and semi-arid regions greatly reduces optimal utilization of water reservoirs. Therefore, applying techniques to reduce evaporation greatly needed. During last decades, a large number of multipurpose dams (258) with overall design capacities of (~898 MCM) were constructed and distributed over the entire Kingdom. Hence, preserving and protecting the stored water dams reservoirs by reducing evaporation is strategic future task of the Saudi government. The present study was conducted for 7 months, from June-December 1998. Experiment was conducted in Riyadh with three US Class-A evaporation pans and a weather station. Fatty alcohol emulsion was selected to reduce the evaporation during summer months in Riyadh. Various concentrations of emulsion substance were used in different pans. First pan (H₀) was filled with water without adding emulsion, while in pan (H₁), Fatty alcohols emulsion was added with recommended concentration of (100 g/1000 m²/day) and similarly in pan (H₂) emulsion was added with double of concentration (200 g/1000 m²/day). The preliminary results of the study indicated that evaporation rate from surface water was reduced overall up to 47.2 and 50.5% in pans (H₁) and (H₂), respectively as compared to pan (H₀).