Now that the weather has cooled down our solar panels are giving us far more energy than we need. This causes the batteries to remain at a charge over 100% all the time. This also means the batteries are going through more water due to the excess energy. I needed to refill the batteries and didn't want to buy a bunch of distilled water in plastic bottles. Instead I tested the difference between our rain water we have caught and distilled store bought water I already had on hand. It turns out our rain water has about 8 PPM while our store bought distilled water as at 11 PPM. Our rain water actually has less particulates than Shure Shine store bought distilled water. Needless to say I filled my solar batteries up with rain water and have no plans to purchase distilled water gain.