A pervasive diffusion of wireless sensors distributed in the environment can be sustained by a significant reduction of the cost of the transducers. Water represents a fundamental resource whose management can be optimized by real-time monitoring, especially in agriculture (irrigation). To this aim we present a low-cost flexible pipe sheath to detect water leakage, as well as conductivity and temperature, by means of contactless impedance measurements. Finite-element simulations show the potential to detect water leaks as small as 1 liter across a pipe length of 2 m, corresponding to a 1% change of a 5 kΩ impedance at 1 kHz, easily detectable by off-the-shelf impedance chips.