Our 3rd "What is it?" was also a bit challenging, as some but not all of our commenters got it right. When we moved in, we didn't have any hot water in our kitchen sink--we still don't in our bathroom sinks. This picture is the hot water heater and tank for the kitchen sink; there's no concept of a central hot water heater supplying the entire house around here.
So, if you're the one responsible for washing dishes at your house, you're probably thinking, "Dude! That's barely enough water to fill up the sink!" Yep, that's about right. We wash dishes one sinkful at a time. But at least we have hot water now and don't have to boil water to wash the dishes. That's a blessing.
Hmm, that's different.