[macksd]

My house has a non-potable water supply used for irrigation, and is in fact required by the town to. I know the same is true in some parts of Utah and probably other places. In such cases, also requiring toilets to be supplied by the non-pot line would be a trivial cost that would pay for itself eventually.

[Nextgrid]

If you’ve already got it then it makes sense to use it, but this doesn’t remove the cost of building and maintaining separate infrastructure at all.

In some cases it might be worth it or necessary, in others I think the process of processing & delivering potable water could be made (or is already) so efficient that building & maintaining separate infrastructure for non-potable water would be a net negative both in terms of cost and environmental impact.