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Water Planning & Distribution

Groundwater Basics

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Click the Fluent Water Facts above to learn more about Colorado’s groundwater and the challenges it poses.

What is groundwater?

Groundwater does not take the form of underground lakes and streams. It is, essentially, saturated rock, and so knowing the geology of the area is crucial to understanding its water. Most groundwater is located in very small water-filled pore spaces between rock grains in sedimentary rocks, between sand and gravel particles in alluvial deposits, or narrow crevices such as fractures and faults in crystalline rocks. Some of these cracks are as small as a human hair.

Groundwater is stored in aquifers. An aquifer is a layer of saturated rock through which water can easily move. Aquifers are everywhere – under the plains, mesas, and mountains. But aquifers vary significantly in the amount of water they hold, their depth underground, and their availability for use by humans.

How does groundwater accumulate?

It all starts with water on the surface. Precipitation can work its way through the soil quickly, but it takes longer to infiltrate the rocks below. Groundwater in the Denver Basin has taken thousands of years to accumulate. Rain and snowmelt continue to recharge aquifers today, but the depth of the aquifer and the type of rock affect these recharge rates. In some cases, this process takes so long that precipitation does not impact the amount of water stored in aquifers, and the groundwater is considered essentially non-renewable.

Types of Groundwater

Tributary groundwater is hydraulically connected to a surface stream and can influence the amount or direction of flow of water in that stream. Water in sand and gravel alluvial aquifers adjacent to major rivers is an excellent example of tributary groundwater.

Non-tributary groundwater is typically produced from aquifers geologically confined such that they have little physical connection to surface waters.

Designated groundwater under natural conditions does not recharge or supplement to any significant degree continuously flowing surface streams. This legal definition refers to eight basins created by the Colorado Ground Water Commission. All eight are located on Colorado’s eastern plains. Designated groundwater is a type of non-tributary water.

Water Origin Resources

The Citizen's Guide to Where your Water Comes From explains how weather patterns and aquifers supply the water we use. Learn more about the intricate distribution systems Coloradans have developed to deliver water to our farms and cities.  Flip through the online version or purchase a copy.

Citizen s Guide  4a40f4c93383c

The Citizen's Guide to Colorado's Transbasin Diversions highlights the history, costs and benefits of these controversial water projects, from both an historic and current point of view. Flip through the online version or purchase a copy.

Transbasin Diversions


1750 Humboldt Street, Suite 200
Denver, CO 80218