I just finished adding a "backlight" to our fresh water tank. If you followed this topic you might remember I installed a "thermometer-like" viewing window in the face of one of our dinette benches so you could see the water level in the fresh water tank under the bench seats. The idea didn't work out as well as I had planned -- there wasn't enough light
in the tank to see the water in the tank.
This weekend I added an LED light
strip that "backlights" the tank when I push a button next to our water pump switch. Now I can see the water level really, really well!
I used a hot-melt glue gun to mount this 2-watt red LED light
strip to the bottom edge of a scrap of pressboard (on the bottom edge so the light comes up through the water instead of shining down on it) and duct-taped the panel to the back of the water tank opposite the "thermometer" viewing window.
Now I can see my fresh tank water level at the push of a button!