Water has an amazing property in that it strips its immediate environment of the minerals its needs to be 'healthy'. Water attempts to make itself as 'healthy' as possible at all times.
When we drink water that isnt at its full health it strips our bodies of the minerals and elements it needs. It therefore depletes us of essential nutrients and minerals, even if it may quench our thirst.
Rain water does not contain all essential elements for the waters full health therefore it will strip the body of these missing components. Drinking rain water, in the long term, is therefore not a good idea.
However there is some good news!
If you suspend a bag of granite dust, or other highly mineralized substance in a non degradable bag withing your water storage device, then it will give the water all the health it needs. Simple and effective, Storing water in egg shaped terracota amphora (as the Romans did) is even better, as it creates spirals in the water which also give the water energy.
Check out Viktor Schauberger's work on watrer collection and storage.. his book the water wizard is available as free download from
www.scribed.
Spring water is best, then well water, then rain water. Drinking distilled water for any length of time is very bad for you.