I'm in agreement. You also need to look at the source of that rainwater. Asphalt shingles? That could be an issue. Then, there is the bacterial contamination. If I used rain water, I would first pass it through a particle and biological filter. These can be made from readily available PVC fittings, a 5 gal bucket, and some sand, hay, and charcoal. You would have to do a google search for the how to. My son took supplies on a mission trip to South America to make filtration systems for families. These systems were used to provide clean water instead of the families relying on contaminated water from rivers and streams.
Bottom line: if you use your well water for your own drinking and cooking, then your animals can drink it. My water is not the best. High Manganese and Iron. Also a bit on the hard side. For the most part, we buy our drinking water, but the animals drink it, as do I on occasion.