No, we want water efficiency. Agriculture has access to cheap water, thus no incentive (nor the economic ability to invest for equipment) to conserve it.

If they would get water at the normal price, their goods would all increase in price, but from a higher price with the same profit margin they'll be able to save for water saving technologies, which will allow them to increase their margin further (or offer lower prices - as eventually everyone will invest in water conservation methods).

And then cities will have more water and food will cost a bit more.