Is the tank half empty or half full?

Like most boats I assume, our 47 gallon water tank is filled through a stainless steel fitting on the deck. Once the tank is full, we have found, without really being crazy conservative, that our water will last about a week. Using past info we were able to guess when we were getting close to having it empty, but we were never quite sure exactly how much was left at any one time.

While running the wires for our windlass, we noticed that when we removed the medicine cabinet in the head we could see the water level in the tank. Now, after cutting a little hole in the back of the cabinet, which I will be covering with a small piece of plexiglass that I purchased, we can easily check to see the state of our water supply at any given moment. The water level is not super easy to see but with the help of a small LED flashlight which we now keep in the cabinet, it works. Yes, there are higher-tech solutions available but I like simple things!