In most jurisdictions—including Seattle—when water heaters are installed, if damage could be caused by leaks from the heater, a pan with drain is required to be installed.
These pans are a great idea for both water heaters and washing machines. Second floor laundries are very common in homes today. Leaking of the washers and water heaters can result in an unbelievable amount of damage in a very short period of time. Installation of a pan and drain is relatively cheap insurance against such damage.
This first picture is of drain and pan installation in new construction for a second floor laundry.

This second picture is of a pan under a water heater. However the hole was cut so that a hose could be installed on the drain to drain the tank eliminates the function of the pan. Elevating the tank in the pan would have eliminated this problem and now a new pan will need to be installed.

Sometimes when you have a tray under the water heater, your first clue that there is a leak is when you notice the cat or dog using it as a watering dish.
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I had a water heater installed by Lowes about 18 months ago…for the last 6 or 7 months, there has been about a half inch of water in the drip pan that I placed under the water heater (it is located on the concrete basement floor by the washer and dryer, so no floor worries). After several contacts with subcontractors and sucking the water out with a shop vac, Lowes and the sub assured me that the drip pan is just collecting “normal” run off and there wee no worries. It is not alot of water BUT, my water heater has basically been sitting in standing water for almost a year and a half now…won’t that rust out the bottom of the water heater???
Hi Matt, I seriously recommend a second or third opinion—there should never be any water in the pan. If they have the TPRV drain going to the pan that is wrong in most jurisdictions, if it is leaking for any other reason that is wrong, and if the TPRV is leaking that should be repaired as well. Is there an expansion tank?
Mr Buell, I’ve purchased the Samsung front load washer with a base of 30″ x 29″
Most overflow pans with side drain won’t accommodate this size washer (or they have a low side wall for the pedestal stand which is an option)
Can you recommend a pan/tray manufacturer with an inside dimension of 31 x 32 or a little larger that I can still install the side wall drain thru?
Plastic is preferred unless you like metal
Most washers are smaller than that—so I ave no idea. Time to start googling I guess.