Water distribution networks are large complex systems that are affected by leaks, which often entail high costs and may severely jeopardize the overall water distribution performance. Successful leak localisation is paramount in order to minimize the impact of these leaks when occurring. Sensor placement is a key issue in the leak localisation process, since the overall performance and success of the leak isolation method highly depends on the choice of the sensors gathering data from the network. Common problems when leak isolating in large scale highly-gridded real water distribution networks include leak mislabelling and large isolation areas obtention due to similarity of the measurements, which may be caused by topological issues and led to incomplete coverage of the whole network. The sensor placement strategy may minimize these undesired effects by setting the sensor placement optimisation problem with the appropriate assumptions e.g. geographically cluster alike leak behaviors, taking into account real aspects of the practical application such as the acceptable isolation distance. Here, a sensor placement methodology considering these assets and a general sensor distribution assessment method for leak diagnosis in water distribution systems is presented for a real District Metered Area (DMA) located within the Barcelona water distribution network.