On other EarthDates, we talked about how humans have used, and sometimes overused, water from aquifers—to grow crops or build cities where previously none could exist.

It might surprise you to know there are also many places where we’re putting water back.

This aquifer management takes many forms.

Perhaps the simplest is called conjunctive use. That means providing surface water, during wet times, to users who would normally pump groundwater.

Another method is called managed aquifer recharge. It routes surface water into man-made or natural infiltration basins, where it can gradually seep into the aquifer.

Perhaps the best example of this channels floodwater away from population areas and into recharge ponds.

Surface infiltration has the added benefit of purifying the water as it percolates through layers of soil and rock.

In the most elaborate method, called aquifer storage and recovery, water is pumped directly into aquifers to stabilize or reverse groundwater depletion.

It has been used in coastal areas to stop saltwater from gradually entering aquifers and replacing freshwater.

Long-term studies show these practices are working. In California, water tables would have dropped hundreds of feet deeper without aquifer management. In parts of Arizona, they’re actually rising.

This doesn’t mean we can get cavalier about freshwater use. But it does show how human ingenuity can address critical environmental problems.