What Is Groundwater? Discover the Hidden Water Beneath Our Feet!

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Did You Know... That There's Water Hidden Underground?

Whether you're standing in the middle of a desert in the Arizona, walking through a forest in Oregon, hiking in the mountains of Colorado, or driving past farmland in Illinois, there's a good chance that water is moving somewhere beneath your feet.
It's called groundwater, and it is one of the most important natural resources on our planet.

Groundwater occurs beneath the Earth's surface in nearly every part of the United States, and across the world. It supplies drinking water to billions of people, supports agriculture, feeds rivers and wetlands, and helps sustain ecosystems.

In some places, groundwater is only a few feet below the surface. In others, it can be hundreds, or even thousands, of feet underground. Although we rarely see it, groundwater plays a huge role in keeping our planet, and us, functioning.

But where does this underground water come from?

How does it get there?

And why is it so important to understand what's happening with it?

Let's take a closer look, starting with the basics, and then exploring more specific groundwater systems beneath the American Midwest and Southwest.

What Exactly Is Groundwater?

Groundwater is water that exists, well, underground! It fills tiny openings, pores, cracks, and spaces within soil, sediment, and rock. Despite what many people imagine, groundwater isn't usually just sitting in enormous underground lakes or rivers. Instead, it is stored within the pores between sediment grains and inside fractures in rock.

Think of a sponge.

When you pour water onto a sponge, it enters the tiny spaces inside and becomes stored there. Many underground geological formations work in a similar way.

These water-bearing formations are called aquifers. An aquifer is a geological layer or collection of materials that can store and transmit groundwater in useful quantities.

Some aquifers are made of sand and gravel, while others occur in porous sandstone or fractured limestone.

Occasionally, groundwater can be seen above ground if the water table is higher than the local geography, like a pond in a valley, or pushed out of the ground by pressure in an artesian well or spring.

Groundwater is found on every continent, including beneath some of the driest regions on Earth. However, not every location has an accessible supply of freshwater, and some groundwater is too salty, too deep, or otherwise unsuitable for human use.

How Does Water Get Underground?

Groundwater exists as part of the water cycle. When rain or snow falls, some water flows across the land into rivers, lakes, and streams.

Another portion infiltrates the ground. It moves downward through soil, sand, gravel, and sometimes fractured bedrock. Eventually, water can reach the saturated zone, where the openings within the soil and rock are filled with water.

The upper surface of this saturated zone is called the water table. The water table isn't at the same depth everywhere. In some areas, groundwater may be only a few feet below the surface. In other places, it may be hundreds of feet underground.

The amount of water that enters the ground depends on several factors, including rainfall, snowmelt, soil composition, vegetation, slope, and geology. Groundwater can also move underground, sometimes very slowly, toward springs, rivers, lakes, and eventually the ocean. In other words, groundwater isn't always sitting still, all alone down there. It's all part of a much larger interconnected natural water system.

Groundwater Exists All Over the World

In tropical regions, frequent rainfall can help replenish groundwater supplies. In mountainous areas, snowmelt can seep into the ground and recharge aquifers. In agricultural regions, groundwater often provides an important source of irrigation and drinking water.

Even in deserts, groundwater can be found deep beneath the surface, sometimes stored in underground formations that have accumulated water over thousands of years.

Interested in aquifers around the world? Check out this list of aquifers by country.

The Midwest USA Has an Incredible Underground Water Supply

I live in Arizona, but have spent a lot of time in the Midwest USA, and it's really interesting to look at the details of the places I visit, for example, the water situation in these areas.

Beneath states like Illinois, Wisconsin, Iowa, Indiana, and Michigan are extensive groundwater systems that provide water for households, farms, businesses, and entire communities.

One particularly important example is the Cambrian-Ordovician aquifer system.

This groundwater system extends beneath parts of the upper Midwest and consists of several sedimentary rock formations, including sandstone and dolomite, that can store and transmit groundwater.

Groundwater is an important source of drinking water for communities throughout the Midwest. The Chicago region, for example, historically relied heavily on groundwater from deep sandstone aquifers before shifting much of its supply to Lake Michigan. That transition happened partly because groundwater withdrawals caused water levels in some deep aquifers to decline significantly.

Even areas surrounded by lakes and rivers can face groundwater challenges.

Learn more about underground water resources, watersheds, and more through sites like the Illinois State Water Survey, the Wisconsin Groundwater Coordinating Council, and the Iowa Geological Survey.

What Does the Ice Age Have to Do With Groundwater?

One of the coolest facts about Midwest geology: much of the region was shaped by glaciers during the Pleistocene Ice Age. (You probably already knew that though, right?)

As glaciers moved across the landscape, they scraped, transported, and deposited gigantic quantities of sediment. When the glaciers melted, they left behind thick deposits of sand, gravel, silt, and clay. These deposits created an underground geological landscape that varies dramatically from one location to another.

Some layers allow groundwater to move relatively easily. Others act as barriers that slow or restrict groundwater movement. For example, sand and gravel deposits can make excellent aquifers because their connected spaces allow water to flow. Clay-rich deposits, on the other hand, often have very low permeability and can limit groundwater movement. This is one reason why two neighboring communities can have very different groundwater conditions.

Don't hate the glaciers for making the Midwest geologically flat and boring! They did a lot to shape the underground water system residents depend on.

The Southwest USA Faces a Very Different Groundwater Story

While groundwater is an important water source throughout the Midwest, it plays a different role in the dry Southwest. Cities like Phoenix, Arizona, receive much less rain than most Midwestern communities. Therefore, they can't rely on groundwater alone to meet their water needs.

Instead, Phoenix gets water from several sources, including groundwater, rivers, and water brought in from other areas. Using different sources helps provide enough water for homes, businesses, and agriculture, especially during dry periods.

Groundwater can become a concern anywhere when people use it faster than nature can replace it. This can cause water levels underground to drop over time, making it harder to access in the future.

Unlike the Midwest, where more rainfall helps replenish groundwater more often, the Southwest has a much drier climate. This makes it important for places like Phoenix to use and manage water from multiple sources carefully.

Learn more about how Arizona manages its water resources through the Arizona Department of Water Resources.

Can Groundwater Ever Run Out?

Not to sound alarming, but things are becoming concerning in many places.

Groundwater may be hidden underground, but it isn't unlimited. Aquifers are replenished through a process called groundwater recharge. Recharge happens when water from rain, snowmelt, rivers, or other sources infiltrates the ground and reaches an aquifer.

However, as mentioned, groundwater can be pumped out faster than nature replaces it. When this happens, groundwater levels decline.

Over time, excessive pumping can create several problems:Wells may need to be drilled deeper to reach water.
Springs and wetlands can lose their water supply.
Streams may receive less groundwater during dry periods.
In certain geological settings, the ground can sink as underground sediments compact.

This last process is called land subsidence. Groundwater depletion is a concern in several parts of the United States and around the world. Even areas that receive substantial rainfall need to manage groundwater carefully because not all aquifers recharge at the same rate.

The USGS and NOAA have additional information about groundwater depletion and land subsidence that is worth reading.

The Hidden Water Beneath Our Feet

You can see why groundwater is one of Earth's most important natural resources. It connects rainfall, geology, rivers, lakes, agriculture, and communities in ways most people never see.

If you're interested in the study of water, including groundwater, rivers, lakes, and the water cycle. the field is called hydrology. It plays an important role in understanding water availability, protecting water resources, and managing environmental challenges such as droughts and pollution.

Further Research about Groundwater and Water Sciences

If you're considering studying hydrology in college, some great schools in the United States include the University of California, Davis, University of Arizona, University of Nevada, Reno, and University of Illinois Urbana-Champaign. These universities offer programs and research opportunities in hydrology, groundwater science, and water resource management.

If you'd rather research groundwater and hydrology on your own, these are a few interesting books about water I've found:

Groundwater Around the World: A Geographic Synopsis by Jean Margat and Jac van der Gun

- A fascinating journey revealing how this hidden resource connects people, ecosystems, and the future of our planet

Groundwater Science by Charles R. Fitts

- A complete textbook filled with technical and scientific info for study and reference, yet a compelling guide to understanding how groundwater moves, shapes our environment, and sustains life on Earth

Cadillac Desert: The American West and its Disappearing Water by Marc Reisner

- A unique account of how ambition, greed, politics, and the relentless pursuit of water shaped the American West; a book that will forever change the way you look at the western landscape

The Death and Life of the Great Lakes by Dan Egan

- A gripping and eye-opening story of how these magnificent freshwater treasures are being threatened, why their survival matters to us all, and what it will take to save them

The Atlas of Water: Mapping the World's Most Critical Resource by Maggie Black

- A powerful story of water across our planet that understands how this precious resource could influence the future of humanity

Interested in Hands-On Science and Experiments involving Water?

Test your own drinking water for 22 water quality indicators including Nickel, Zinc, Copper, Fluoride, Iron, Chlorine, Chromium, Lead, and Bacteria with this DIY at home water test kit. It's fast and easy and you don't have to send in a sample or anything like that.

Check the moisture content in the soil in your houseplants, your yard, or anywhere else with a simple and accurate moisture meter. Useful if you're a gardener or just curious about how wet the soil is. If you're intrigued by soil as well, this 7 in one meter measures things like temperature and pH too.

Have another fun way to learn about water, other great book recommendations, or fun groundwater facts?  Let me know,  I love to learn too!