The quest for a characterization of water distribution systems in relation to water losses has led to define a series of indicators aimed at identifying the most accurate measurement of the performance by mainly trying to respond to the following questions: how much do the water losses amount to? What is the economically sustainable water losses level? What are the controls which the regulator may impose and on the basis of what parameters? In this paper, we will discuss the performance indicators related to the water losses introduced by the International Water Association (IWA), by the Economic Regulator for the Water and Sewerage Industry in England and Wales (OFWAT), by the Italian legislation (Ministry's Decree n. 99/1997), and, finally, some indicators proposed by the French legislation and by the German guidelines. Each group of indicators here discussed can offer some advantages if compared to the other, but also some weaknesses; in particular, no group seems to respond in the most appropriate way to the regulator's, the provider's, the user's and the public opinion's expectations. The need for a homogenization of the different approaches is finally remarked. Though preserving the local needs and expectations, this process would allow to produce a coherent framework, even at different scales of interest, so as to avoid the impoverishment of the water resources.
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