Impressive. ...and you did this why?
One of my cars - might have been the 2010 Prius - had a flexible plastic tongue about 8 inches long with graduations molded along its length that was attached to the inside of the cap. Unsnap the cap and pull up until you saw the wetted section, thus understanding how much fluid was left. With my Volt I just fill to the neck every four to six months - or just before departing for a road trip. It doesn't have to be a problem, if you don't want it to be. 8^)THE PROBLEM is in GEN 1, not only we do not have water level monitor(except 2011/some 2012), but we cannot see the water reservoir at all...totally hidden from the operator!!!. Perhaps using a mirror ?. Hard to believe such poor engineering design something of such common use as windshield washer fluid.