So very, very, confused.

I'm really perplexed tonight. I came home from work and as I walked through the kitchen, I walked right through a puddle of water. A fairly good sized puddle. And the strange thing is that I can't figure out where it came from! It wasn't there when I was home at lunch. I looked down...nothing spilled, no tell-tale trail. I looked up...no hole in the ceiling! So I mopped it up, trying to shake this odd feeling. Had someone been in my house? Nothing was taken. Unless....the man who lives in my basement has a young son who just came back from his summer holidays. Last year he got locked out of the basement NUMEROUS times and I would let him use the phone to call his dad. This is the only thing I could think of...that he let himself in (we lock the outside door, and I leave my inside door unlocked)thinking he could use the phone, then maybe spilled some water from a water bottle? It's a long shot....and I hate to blame him...but what other explanation could there be???? Needless to say, I locked the door when I went out tonight.