One of the important tasks when designing the water fittings is to calculate the orifice area of locking pair for passing the calculated water flow at a calculated pressure. The method of determining the orifice area with smoothly changing shape based on the piecewise-element method is proposed. This method is characterized by a comparative simplicity and sufficient accuracy for engineering calculations to determine the orifice area of the disk type locking pairs for the valve head. The proposed method allows us to determine the required size of the orifice area for passing the calculated water flow and also to determine the water flow rate depending on the opening level of orifice. The authors carried out the necessary calculations and manufactured ceramic disk type locking pairs by using the proposed method. Bench tests of water fittings with valve heads those are having orifices with smoothly changing shapes (in the form of bent blob) showed that water flow is changing almost in proportional to the tap opening. This method can be used not only for the designing of the water fittings and also for the shut-off valves of various purposes. © 2016 Journal of Urban and Environmental Engineering (JUEE). All rights reserved.