We already reclaim a great deal of the water at our treatment plants but i believe the vast majority is used for irrigation rather than re injected into the aquifers despite it be clean and sanitary.
We have a huge garden on our hobby farm and we have to irrigate (high desert). T-tape is amazing stuff and it puts the water right on the plant. Combined with heavy compost and wood chips on the pathways we have cut our water usage every year (from our well) even as the garden gets bigger.
Large scale farms requiring irrigation will adapt and become more efficient in the future because there is some truth to the fact that we are exceeding the sustainable rate for pulling water out of the ground for horribly inefficient irrigation systems. Drip systems that put the water directly on the plant/roots are extremely efficient as is the use of mulch for conserving water. The systems they use for orchard irrigation and grapes around here are pretty efficient and the return on investment is making more people switch.