Water fittings are a necessary element of equipment for building plumbing systems. One of the main technical characteristics of water fittings is their regulatory capacity. Currently, valve heads with flat ceramic locking elements are widely used in plumbing systems. Ceramic locking elements work with a high abrasion resistant and without water leaks. Regulatory capacity of flat locking elements depends on orifice shape. Valve heads that are equipped with flat-locking elements with semicircle or sector-shaped orifices have a low regulatory capacity. When the tap is opened or closed, the water flow changes abruptly with a slight turn of the handle. The water consumer is forced to spend more time in controlling the water flow with a desired temperature without using the water. As a result, clean tap water flows into the sewage system without actually being used, which is unproductive expenditure. The application of a flat locking pair with a smoothly changing shape is advisable to improve the regulatory capacity of water fittings. This form of orifice allows to change the water flow in proportion to the rotation of valve head handle. The proposed method of calculation allows to determine the orifice area to design the valve and its geometric parameters. The use of water fittings with a locking pair that is calculated by the proposed method can reduce the water loss by 12…15 % compared to other types of valve heads.