No matter how many times I hear Toto “bless the rains down in Africa,” I’ve never thought of the continent as a water-rich place. Perhaps it’s the fame of the Sahara desert, the nature documentaries depicting wildebeest migration on the savannah, or the harrowing tales of East Africa’s drought – but I’ve always conjured dry, dusty visions instead.

So when I heard that a vast new underground water supply had been found in Kenya’s Turkana region, I was intrigued.

The five aquifers — each lying more than 100 meters below the Earth’s surface — supposedly contain as much as 66 trillion gallons of water, the equivalent of 100 million Olympic swimming pools. They were discovered using new techno-savvy approaches that combine satellite imagery with traditional geological and hydrological surveys to predict areas where water ought to accumulate belowground. (So far, two of the five aquifers have been verified using test wells.

The prospective water supply increases Kenya’s known water reserves by 17%, and is a boon in a country where more than half the population lives without adequate sanitation, and four in ten people lack ready access to drinking water. The United Nations — which, together with the Japanese government, helped pay for the water prospecting — hopes that the water will also help irrigate crops, reducing hunger and food resource conflicts.

Despite billing as a potential salvation for the drought-ridden region, though, the new water supply should come with a list of caveats. First, the aquifer depth means that foreign investors will have to bankroll extraction infrastructure. Second, the aquifers refill only through slow accumulation of rainfall, which percolates through the soil into the water table. Weather events can be sporadic, however, and even with steady, generous rain, it would take 75 years to re-accumulate the water held in the aquifers. So if the Kenyans use more than about 1.5 million swimming pools-full of water a year, they’re using the resource at a non-sustainable rate.

At least these aquifers do seem to replenish themselves, however. Plenty of other areas around the world use “fossil” water supplies — belowground freshwater stocks that were formed thousands, or even millions, of years ago. These one-time use stocks have supplied tremendous growth in water-poor regions, but their tenure is fragile. In coastal areas, depletion of groundwater supplies can result in salt intrusion, as ocean water seeps in to fill in the gaps. Excessive water removal can also change the ground’s physical stability, causing shifts and tremors as the ground settles over new air pockets.

But the greatest threat, of course, is the one to water security. What happens when water supplies dwindle?

In the United States, we use just under 80 billion gallons of groundwater each day. The new Kenyan aquifers would last us just two years and a few months. Of course, our own freshwater supplies are much larger, but that hasn’t stopped us from depleting them by about 264 trillion gallons.

Despite increasing awareness of limited freshwater supplies and new conservation technology, we continue to deplete our groundwater supply by a further 6 trillion gallons each year. California’s Central Valley, just next door, is 38 trillion gallons in the hole. In some areas, the local water table has fallen to 30 meters below sea level.

Across the country, we’re using water at an unsustainable rate.

And in some areas, especially given drought conditions like the ones we experienced last year, that means a tough re-evaluation of water rights. How do you regulate access to a belowground supply that doesn’t follow surface political boundaries?

Texas, at least, knows how it shouldn’t be done. Keen to protect the property rights of its citizens, the state uses the “Rule of Capture.” Regardless of who shares the water supply below your property, the right to its use depends on who can pump it out the fastest. This pits neighbor against neighbor, ultimately destroying a public good.

Most other states own their groundwater, and choose to allocate it according to the needs of various interest groups – cities, farmers, and so on. Still, as climate change shifts rainfall patterns, compounding the emerging issues of water resource exhaustion, decision-making across the country, and across the world, will only become more complex.

Prospecting for new water supplies might provide stopgap relief for some human suffering, but it can also bolster unsustainable growth, producing a sharper crash in the long run. We should be mindful of this before drinking to (or drinking up) our new discoveries.

Holly welcomes reader questions, comments, and other feedback at hollyvm “at” stanford “dot” edu.