This is a great question with several different ramifications and conditions.
The question illuminates the reality that the world gets a voluminous amount of water from rain, which runs all over the place as what we call storm water. In most geographies the majority of our rain/stormwater winds up flowing to streams, rivers and lakes, and eventually out to our oceans or into the atmosphere by way of evaporation. For sure in places where there are water shortages capturing this water makes sense.
Recharging aquifers is a challenge on a few fronts.
- The known aquifer recharge points are often not known
- The recharge points that we do know are more often than not, too small to allow the high-fill flow rates that would be required to significantly add water to the aquifer.
- Stormwater abundance happens only during the storm and then for a short time after the rain has subsided. In order to fill an aquifer we would first have to create the huge infrastructure to collect it, contain it, filter it as necessary and then pump it back into the aquifer.
Think about this; one inch of rainfall collected over a 1 acre space will deposit roughly 27,000 gallons of water.
As an example, my town, Memphis, Tennessee pumps roughly 200 million gallons of water per day from its aquifer. Doing some simple division we see that to make up for the daily water use here using stormwater Memphis would require the collection of 1 inch of rainfall over roughly 7,500 acres of land, each and every day.
So the questions become;
How do we divert, contain and collect water from 7,500 acres?
How do we get it to rain one inch each and every day?
How and where would we store 200 million gallons of water…..each and every day?
If we did have a 200 million gallon reservoir where would we pump it all in 24 hours? Where would we find aquifer entry points that could accept 200 million gallons per day? Think about this, in order to pump 200 million gallons back into our aquifer would require pumps running 24/7 @ 140,0000 gallons per minute flow rate would be required.
The costs of the infrastructure, pumps, workers and energy to collect and move this water would be mind boggling and prohibitive. Also remember that stormwater contains dissolved herbicides, pesticides, oil, gasoline, dirt, feces, landfill leachate, and litter from our streets that is also infested with drug needles, diapers, decaying vegetation and fertilizers.
If we could capture, contain and pump this back into the top of an aquifer, (yuck), would we really want to? Also remember, that whether we like it or not, because stormwater runs everywhere, and because aquifer recharge points are located all over the place, a lot of this nasty water is already recharging our aquifers.
There are places where the collection of rainwater with conversion into potable water makes sense. Dry, desert areas where there is a lot of surface area and not a lot of polluting and interfering structures are the best candidates. However, even then, this process it still prohibitively expensive, design-intense and demanding of forward-looking vision such as that contained in this most excellent reader question.
On a final note, why would anyone want to recharge an aquifer? What is the point of this? Why expend the money and engineering effort when it is much cheaper just to build new ground-level reservoirs and storage tanks to hold the water and then simply send it to the local treatment plant to be processed into drinking water?