[TomVDB]

I don't think it makes sense to look at the total supply of water and use that as a starting point of the savings. The total supply of water is only useful in the context of a discussion of multi-billion dollar infrastructure improvements to expand the ability to transport water from one place to the other.

What really matters is the amount of water that can be channeled to your place of living today.

And then having small changes like non-flushed toilets help increase awareness about water shortage. If that ultimately makes people replace their lawn with desert plants, I think it's a win.