Whenever there is a leak and I’m not sure where it’s coming from I clean the area to ensure it’s dry and lay a large piece of paper down to locate the leak and note the timing (to get a sense of how fast it’s leaking). Then take pics so I can see where the water is in relation to the pipes or whatever.
For example, I have a leak under my sink that was really fun (sarcasm) to discover. I cleaned it all up with paper towels then laid a large piece of paper down. (It’s amazing how often children’s easel paint paper comes in handy!) Wrote down initial time stamp on scrap of paper (5 mins, 10 mins, etc.). Now I have a sense of where to lay down my buckets as well as a pic to email my landlord to help him figure it out. By the way, it looks like I moved the paper around and it caused all this zig-zagging—that is not true. I simply laid it down. My theory is that someone is trying to communicate with my by writing from the great beyond.
Here’s my pic to demonstrate:
You With A Clue 