Leakages are a relevant issue in water distribution networks with severe effects on costs and water savings. While there are several solutions for detecting leakages by analyzing of the minimum night flow and the pressure inside manageable areas of the network (DMAs), the problem of estimating the time-instant when the leak occurred has been much less considered. However, an estimate of the leakage time-instant is useful for the diagnosis operations, as it may clarify the leak causes. We here address this problem by combining two change-point methods (CPMs) in a hierarchy: at first, a CPM analyses the minimum night flow providing an estimate of the day when the leakage started. Such an estimate is then refined by a second CPM, which analyzes the residuals between the pressure measurements and a network model in a neighborhood of the estimated leakage day. The proposed approach was tested on data from a DMA of a big European city, both on artificially injected and real leakages. Results show the feasibility of the proposed solution, also when leakages are very small.