This chapter focuses on the difficulties of measuring leakage in water infrastructures. With leakage reduction essential to transforming water infrastructures from intermittent to 24/7 water systems, World Bank consultants in Mumbai worked hard to apprehend and arrest water leakage in the city. Nevertheless, their attempts to derive leakage figures were challenged by the material and political situation of water infrastructure in Mumbai. As measure is constantly rendered precarious in Mumbai’s water network, the chapter turns to focus on the practices of engineers to regulate leakage in the city. These practices reveal a far more tenuous, improvised, and compromised form of expertise through which engineers constantly struggle to control the pipes of the city.