Install a Drain Pan to Catch the Flood

You should install a drain pan - sometimes called a drip pan - under every water heater or clothes washer, to catch any leak and direct it away before it becomes a flood. Drain pans are not usually installed under dishwashers because those appliances are typically connected directly to a supply pipe and don't heat the water, thus minimizing the chance of a leak. If you're putting the new heater or washing machine on the second floor or higher, or above your finished basement, consider a drain pan a necessity. That also applies if it's going in your concrete-floored utility room which is just off a room with a wood or carpeted floor.

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Make sure the pan you buy has an outlet tap. A water heater holds a lot more water than any pan you can put under it, and a ruptured washing machine supply hose or a failed tank in your water heater can allow the water coming to the appliance to pour onto the floor until the supply is turned off.

Pipe the outlet to a floor drain or sump pump, if you have one handy.

For an upstairs laundry, install a sanitary tee in the drain pipe for the washing machine, above the plumbing trap but below the bottom of the drain pan, and pipe the outlet to that. If necessary, pipe the outlet down to a lower floor and then tie it into a drain pipe - just be sure there is a trap between the point at which you tie in and the main drain leaving the house.