Using harvested rainwater is not new, it has been in practice for thousands of years (3000 B.C., and may be even earlier).  But we have something that wasn’t available back then; the ability to disinfect rainwater to make it safe for human contact or ingestion.  Harvested rainwater can be safely used outdoors and indoors if the correct steps are taken to treat it. The type of disinfection depends on how the water is going to be used and the requirements of local plumbing codes.  With modern disinfection, rainwater can even be filtered and disinfected to potable standards.