RE: Hot Water question. Thanks

I have been setting my water heater at the same temperature for a while. But the water comes out at different temperatures depending on the days. Some days the water is significantly hotter. I am talking about the same place/sink/bath tub where we use hot water. So it is not that the water in one place of the house is hotter than another part of the house. Also, we have a small place, only 800 square feet.

Could anyone tell me why? I am kind of puzzled. Really appreciate your insight.