Some random potshots...
First, why WOULDN'T one use catchment water for drinking? At least you know where rainwater has been!
And today, with the latest .5 micron ceramic filters (conventional small pore filters are 5 microns) providing a way to sterilize drinking water for only a couple hundred dollars total investment, and $50/year maintenance cost, the threshold is very low to harvesting your own drinking water from the sky.
Second, y'all should get the CTAHR handbook on rainwater catchment. Hard copies are free to residents at the County Extension office in Hilo, and the electronic version is available online free. It is THE go-to reference on the subject.
THIRD (and now I'll stop counting), ferro-cement water tanks are the best, strongest, easiest to maintain, most earthquake resistant tanks you can have. They do self-buffer, so you don't have to throw in a box of baking soda every month to counter the acidity of the rain like you do with steel and wood tanks. The most ingenious ferro-cement water tank for rainwater catchment I have seen yet is the 20' Monolithic dome (oblate spheroid shape, half dome) at the home of David B South in Italy, Texas. It's self covered, earthquake and tornado proof, vermin proof, etc. Wish I could find someone locally to build me one like that.
It is true that drinking only rainwater can leach down the minerals in your body, the same way drinking distilled water does, because it is inherently very pure. That can be easily corrected with inexpensive mineral supplements, by eating mineral rich foods like lots of leafy greens, and/or by switching to sea salt for cooking and table use. Purified table salt is 99.9% sodium chloride (salt), whereas sea salt is about 88% salt and 12% other nutrients and is mineral rich. It is the original mineral supplement.
And finally, to return to #1, unfortunately you have no guarantee that county water is safe by the time it gets to you. I LIKE being able to manage my own water safety, because I'm more invested in it being right than anyone else is.
Okole maluna! [:o)]