Why would it leak water one day and not the next day

It may have all leaked out. I'd check the coolant level and top off with water first. If it was very low and it starts to leak again, you can rent a coolant pressure tester to find the leak. It's a tool that pressurizes the system so you can check for leaks without running the engine. This also makes it so you aren't working on a hot engine while trying to find the leak. Alex