Few people need to be reminded of water’s importance. Along with energy, it is essential for everyday life. Water provides sustenance, supports industry and irrigates fields. But city administrations are struggling to meet rising demand from growing populations while contending with issues such as water quality, flooding, drought and aging infrastructure. This chapter will give cities tools to apply smart technology for an economical and sustainable water supply. It begins by outlining urban water realities. Next it explains the benefits cities can achieve by increasing the intelligence of their water systems. Finally, it talks about the technology targets cities should aim for to gain those benefits. We need water for human consumption, of course. And to produce food. But not everyone realizes we need large volumes of water to produce energy. Thermoelectric power plants boil water to create steam to drive electricity-producing turbines. In 2005, U.S. power plants withdrew four times as much water as all U.S. residences, accounting for 41% of total water use. The so-called “energy-water nexus” works in both directions. It takes a lot of water to create electricity. It takes a lot of electricity to pump and treat water. Worldwide, we use an average of 7% of total electricity to pump and treat water and wastewater, but the percentage can be much higher.