A systematic investigation was conducted to test the efficiency of 53 commercial water repellents. Through analysis it was possible to identify the chemical structure of each of the products, its concentration, and the manufacturer of the more widely used chemicals. Four different supports (brick and three limestones) were used in the accelerated aging test to investigate the longevity and durability of the repellents. The results have indicated the relationship which exists among the chemical composition, the concentration, the nature of the support, and the efficiency of the water repellent; the tests have further demonstrated that there are significant differences among the products with respect to how they affect drying behavior and water vapor permeability.