Yup, there you have it.
A bare steel water heater with an always on element that kept the water temp at an average of 30C, would be able to warm the water to perhaps 50C once the standard insulation was put on it. Once the silver foil extra insulator was in place it might go up to 60C.
Water heaters have enough output to heat water rapidly therefore an always on element would soon lead to disaster. In real life the element is only on enough to keep the water at the desired temperature. An insulated, or double insulated tank needs less electricity or gas to accomplish this because the heat loss to the environment has been decreased.
I know you won't be able to make the jump to Sun (element), Earth (hot water), Atmosphere (insulation) and Space (environment).
But I tried. Again.