The efficient design of valves for the water supply system requires knowledge of the parameters and regularity of change in the hydraulic characteristics of the locking pair. The article contains the results of a study of regularity of change in the hydraulic characteristics of the locking element in the form of a "curved drop" for plumbing fittings. The numerical values and the patterns of change in the hydraulic characteristics of liquid outflow through the hole in the form of a "curved drop", made in a thin wall defined. The patterns of change in water discharge identified, and the comparison of characteristics for different bore shape. The ability to adjustment the flow of water depends on the shape of through hole. The values and regularity of change in the hydraulic characteristics of the locking element in the form of a " curved drop" for water reinforcement obtained on the basis of theoretical and experimental studies. The results of the study are of interest in the theoretical and practical aspects for the design and manufacture of valves for water supply. The results of theoretical and experimental studies show that the form of "a curved drop" for plumbing fittings allows to have a linear change in water consumption depending on the opening tap. The coefficients allow us to design the plumbing fittings valve type with a high regulating capacity. The use of the locking element with a hole in the shape of a "curved drop" allows to reduce the loss of tap water of drinking quality. Water savings for the house for three persons is 12-15% compared to valves of other types. The study is in the continuation.