Was it common practice back in the early 30's to use tap water or distilled water for radiators?[/QUOTE
To respond to the original question:
In the '30's through the early '40's money was in very short supply, a prudent motorist would use well and/or tap water, adding a "coke" bottle of soluble oil, which could be obtained from any machine shop for free, maybe a nickle. If the motorist was flush with money he could purchase a can of rust inhibitor.
In reality the average motorist did not take very good care of his vehicle. The average vehicle was done in two/three years, if that long.
It use to be very common in southern-eastern Idaho to see family farms that had every vehicle they had ever purchased, dating back to the early teens, lined up behind the barn. It was easy to read the good years because the age of the vehicles would generally be about two years apart. In the lean years the ages of the vehicle might be five or more years apart.
One farm I use to know of near Salmon ID had Model T's lines up side by side like cord wood, starting with 1910 through the '20's.
The 1940's/50's saw a big change in the quality of the average vehicle and how people took care of them.