The damp coils also trap airborne solids --if you want to see put some in a container ans evaporate off all the water ---if it is pure there will be nothing in the bottom of the container.
Would you drink this water??
When I had regular batterys I just used tap water ---got 7-9 years out of them.
Battery and coolant water are two different applications. If you have good tap water - soft and minimal solids- then tap is OK for batteries. Distilled is cheap and better. Beware of distilled water for the cooling system. Distilled water or deionized water is "hungry" water. It loves to pick up iron, especially hot iron. We used deionized water in a refinery application with steel pipes in several heat exchangers. After a few years we needed to replace the tube bundles with stainless steel tubes. This was an expensive lesson.
Been using store bought distilled water in the battery and rediator. Battery is an Interstate and is now eight years old and is in the car in New England in an unheated garage and not used or charged from September till July each year. Turn the key and it starts right up every year after sitting for nine months.... The radiator is an original and was re rodded in 1983 and is clean as the day it was rebuilt. Change anti-freeze every three years 50/50 mix and it comes out clean as the day I put it in.
When I got out of the Army in 1971 my neighbor gave me an Interstate 6 volt battery he had laying in his garage. I used it in my 1949 Chevy truck and got over 10 more years out of it, and that was with long periods of non-use and not being charged.
When I worked at the junk yard charging and checking batteries for resale Interstate 12 volt batteries came in last as far as service life. That's also been my own experience with Interstate 12 volt car batteries, and I got less than 6 months out of my new Interste lawn tractor battery. I don't know why Interstate 6 volt batteries were so good, but the 12 volts were so bad.
I collect rain water in two large buckets and when full I filter it into gallon milk jugs. They fit nicely under the bench until needed. I use a piece of old bed sheet as a filter.
Bruce a400usa@nccn.net
I wouldn't use 'dehumidified' water..mabe for plants.
However, RAIN is mother natures 'distilled' water. Drinkable and useable for anything (without minerals)until contact with minerals. Batteries are not built to handle minerals in their liquid mix. Bottled 'distilled' water is cheap, if you are willing to accept/believe that it is distilled..use it in bat/radiator.