Water heater emergencies are never fun, and they never happen when it's convenient. However, if you have a leaking water heater, there are a few things you can do. Turn Off the Water When you notice your leaking water heater, turn off the water supply to it. When you think about plumbing, you likely imagine showers, sinks and appliances. While important, they are not the only parts of your plumbing system you use every day. Modern plumbing systems are made up of numerous components that work together to keep everything running smoothly.