In this paper we discuss sampling design for the calibration of water distribution system hydraulic models. The sampling design for the calibration of water distribution-system models is formulated as an optimisation problem consisting of two normalised objective functions. The first objective function is used to increase the calibration accuracy of the model parameters, and the second one is used to reduce the number of necessary measurement locations. The optimisation problem was solved by using genetic algorithms. The verification and application of the developed optimisation model (called IMMe) were carried out on the artificial water distribution system of Anytown, which serves as a reference model for testing various researches in hydraulic modelling. The verified IMMe model was applied to a real water-distribution system in the town of Sezana. For both water distribution models, the use of genetic algorithms proved very efficient with extremely combinatorial optimisation problems. The developed calibration and sampling design allow very accurate hydraulic modelling of the water distribution systems, which is of key importance for ensuring the economy and efficiency of drinking-water supplies in the future.