The standards needed for non-potable water is much less strenuous then potable water, and so are the chemical and energy requirements.

But I’m not very interested in arguing with you about a subject I have actual experience in. Believe what you want.

Except for the fact that residential drinking water has to be cleaned, filtered, disinfected, & transported to your home all of which has a cost and requires energy & resources. Where as rain water falls on your roof and is simply collected, filtered, and used.

I’ve helped design several commercial scale rain water systems in the US for non-potable uses such as car washing & toilet flushing. It’s a thing.