This paper introduces a methodology that calculates the optimum replacement time for the pipes of a water network. This is done through a technico-economic analysis that takes into account all kinds of costs for the repair or replacement of trouble-causing parts of a network. The applied methodology uses the present value method of economic analysis and suggests alternative ways to specify the models of break rates for the various kinds of pipes. This goal becomes possible using the proven strong relationship between the leaks and breaks that occur in water pipes. Finally, the methodology presents a way of calculating the optimum replacement time for the pipes of a water network, by taking into account the water flow velocities (standard values and variations) in the pipes.