Is it safe for plumbing to use rainwater to flush toilets?
It is doubtful the pH+ of rainwater anywhere, other than directly downwind of an erupting volcano, would be unsafe in terms of damaging plumbing fixtures or pipes.
That said, there is concern in how the rainwater is stored. It must be kept so as not to be a breeding place for mosquitoes, toxic algae or other noxious critters, nor should the container cause entrapment of wildlife. There also must be air breaks to ensure that the untreated rainwater does not enter and contaminate potable water. There may be local regulations regarding use of rainwater or &quot;greywater&quot;.