You probably have heard that California is running pretty low on water. The bad news is that they’re not the only ones with a water crisis at hand.

Although much of the Earth’s surface is covered in water, the majority of the world gets fresh water by pumping it out of underground aquifers, vast bodies of water that naturally occur beneath the Earth’s surface. Recently, NASA set out to determine how much water is left in these aquifers using their GRACE (Gravity Recovery and Climate Experiment) satellites and found that many of the world’s aquifers are “overstressed”, meaning the rate at which we are emptying them vastly outweighs the rate at which they’re being replenished. The worst cases of this include the Arabian Aquifer in the Middle East, the Indus Basin of India and Pakistan, and the Murzuk-Djado Basin of North Africa.

So how exactly does one measure underground water levels from space? NASA’s GRACE satellites are able to measure minute differences in gravity over large areas of the Earth’s surface. These differences in gravity are actually caused by changes in the local thickness and/or density of the Earth’s crust. From this satellite data, scientists can isolate how much of the change is due to the movement of water. This gives us a rough idea of how fast we’re emptying the aquifers. By combining this information with additional data collected by hydrologists (water scientists) on the ground, scientists can then calculate monthly changes in the water levels of the aquifers, as well as how much water is actually left.

Unfortunately, the problem we face is that there’s very little information from hydrologists on the ground because frankly, not much money has been put towards measuring aquifer water levels. So while our satellites are telling us that the aquifers are rapidly losing water, for the most part, we have no idea how much water is actually left!

While we may not know how much water is exactly left in our aquifers, what we do know is that when the water in these aquifers begins to disappear, the ground begins to sink. In the same way you sink towards the floor as an air mattress loses air, when an aquifer loses water, all the soil above it sinks down. To show you just how much the ground can sink from aquifer draining, here’s a picture of a famous scientist (Joseph Poland) standing next to a telephone pole. On the telephone pole are signs showing where a person would have been standing in 1925, 1955, or 1977.

Credit: US Geological Survey

At this particular location, the land had sunken down by about 30 feet! During the 1970’s, this problem was temporarily fixed by building canals to bring water from the wetter areas of California to the drier ones. However, with the current ongoing drought in California, massive sinkholes are once again creating major headaches in the state.

Okay, but even if the aquifers run out (and if you ignore the problems of the ground sinking), won’t we still have the oceans to supply us with water? Well, yes we do…but there’s a catch. The problem is that making freshwater out of seawater (desalination) is currently very energy-intensive. In fact, exclusively supplying water to the US via desalination would increase national energy consumption by 10%, the equivalent of putting an extra fridge in every single household. And that figure doesn’t even take into account the energy requirements for building the infrastructure to pump all that water to the more central portions of the country!

While it may not seem like fresh water should be a major issue for us at the moment, the truth is that it will be soon. The biggest problem is that we’re currently draining our aquifers without truly knowing how much is left. Eventually, we’re going to run out. Whether we work on replenishing our aquifers, improving desalination, or getting better at recycling water, the key is that we start working on it as soon as possible. If not, a global water crisis is all but certain.