While I wouldn't combine the ...

While I wouldn't combine the two, wastewater reuse is a good option in arid areas. What you do with the reuse water will determine the level of treatment needed. Watering animal fodder crops has a lesser treatment requirement and can benefit from left over nutrients, same with consumption crops that the edible portion isn't in contact with the water. Irrigation technique and site access need to be considered. 

Potable reuse requires a high level of treatment. I have seen a system where the wastewater plant effluent treated to a good level (20mg/l max BOD, TSS) is then run through a up flow clarifier and sand filter, 24 hours of contact time with a free chlorine residual of 0.2 mg/l and then used to recharge the aquifer.  The nearest potable well was several miles away.

We have been looking at a similar system, but using micro filtration for the wastewater plant. The aquifer in our area has been declining. We currently produce water to be stored in the aquifer through the drinking water plant during seasonal high water flows. This has slowed the aquifer decline. We may be able to stop the decline if we do the same with the wastewater plant.