OMG! You sound like me! We harvest rainwater for my garden and plan on increasing our rainwater harvesting this year since I want to expand the garden, and we've already begun planning the addition of a water harvesting system on our new coop so the chickens get to drink rainwater as much as possible. My current flock actually prefers the rainwater to tap water. I also don't feed soy or GMO, canola, or even corn to my chickens. After spending fifteen years researching nutrition and seeing what's been done to alter corn I just can't bring myself to eat it anymore, not feed it to my pets/chickens.
I know, even if I grow non-hybrid corn to have a heritage crop it's not a guarantee my neighbor's GMO hybrid corn crop won't cross-pollinate with mine -- thanks to Monsanto and Dupont who have paid to have agricultural laws enacted to fine anyone whose crops have cross-pollinated with their patented GMO seeds. Supposedly GMO was meant to increase the hardiness and output of crops but after 20 years of study the gradual opposite is occurring!