If you removed the water heater there should be only the fresh water tank. There should be a hole in the subfloor in the galley cabinet. In the hole you will find 3 red valves, hot water line, cold water line, and low point drain. There may also be similar valves in the bathroom closet. If you don't have one a Service Manual would be a good idea. You can get a copy from the mothership. At the end of January in New England and if you are redoing the plumbing anyway closing valves is a moot point.
Sail on silver girl. Sail on by. Your time has come to shine.