This is a cheap but functional solution to checking how much fresh water you have.

The easiest place to put this was in the cutout for the V-Berth. I installed a tee in the water feed from the tank, a 90 deg. ball valve and some clear 1/4 inch tubing. Drilled a hole for the valve and a hole for the  top of the hose to tuck into. Glued the tubing inplace with Super Glue. All parts came from Home Depot for about $20.

The valve is opened whenever you need to check the water level. The water level rises or falls to the level in your tank  You can calibrate it when you fill it.