Years ago I was renting a house with a small in-law building in the back which was rented separately. I'd get the electric bill and then split it 75/25 with the

Years ago I was renting a house with a small in-law building in the back which was rented separately. I'd get the electric bill and then split it 75/25 with the guy who lived there. Over time the electric bill kept getting higher and higher, until it was like $500+ a month. I talked to the landlord and the other renter about it and none of us could figure out what was drawing so much electricity. I called the electric company several times, and they'd asked if I had shut off my pool, which I didn't have, or if I had been using the jacuzzi a lot, which I also didn't own. Then they asked about power tools, welders, and all sorts of other things, and when I finally convinced them something was wrong they sent someone out. The electric guy did the obvious thing: He started flipping breakers to see which circuit was drawing so much electricity. I had done that as well, but had no idea what to do from there. He was able to follow it out to the in-law house, which was in complete darkness as it had zero electricity inside - except for a tiny water heater installed out back. It had somehow gotten filled with sediment, so the heating element was basically trying to keep a barrel full of sand warm. (The guy who lived there just assumed the hot water tank was small and took fast showers as a result). The landlord replaced it and suddenly the bill went down to less than $100. Crazy. The point to this story is that there's probably a lot more that could be done before worrying about recouping the heat from your bath water.