I want to move my hot water heater to the porch by my washing machine. Can I use the same water supply lines that are used for my washer?
Theoretically, it's possible. Practically, it depends on the size of the pipes, distance, and layout of your plumbing. If the water main is 3/4" and the washing machine is fed by 3/8" lines, you'll lose a lot of flow going out and back. Depending on the type of valve on your shower, it could mean significant temperature swings when a toilet is flushed or another shower is running, or you could see the flow frequently drop to a trickle to avoid freezing you. It could also mean much longer waits before hot water reaches various fixtures.