Hot Water/Lack of Hot Water

I am very picky about the temperature of my shower. This is one of those bad habits you acquire after a lifetime spent solely in a developed country that has things like water heaters and carpet. Most of my showers are spent making tiny adjustments to the temperature of the water. Someday, I want to commission a temperature gauge where you can adjust the temp of the water by individual degrees with a button.

Today, I'm showering and wondering why it got colder instead of hotter when I turned the knob. After a minute of wondering, I look down. I am nudging it towards the blue side and not toward the red side.

Then, I have a little tingling, crawling sensation on my back, thinking about the last time I took a shower. The tingling kind of reminds me about the time when I had a spider on my back in the very same shower (typing that, I had to slap my back a few times. Ick. Ick. IckIckIck.) I'm betting that the last time I took a shower that it was NOT getting colder and colder because the hot water ran out.