You may be surprised at how much this is already being done.
The Orange County (Calif) WWTP has been pumping discharge into the ground to replenish the aquifer for over ten years.
We are talking about millions of gallons per day.
'Water Reuse' is big in Calif., Arizona, and other states.
With some degree of treatment, I trust. Otherwise, it’s going to be pretty darned sludgy. They do this with raw sewage?