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Water Planning & Distribution

What is an Aquifer?

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

Nature’s Underground Water Storage

Aquifers store groundwater. 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. Geology often defines how this water moves and can be accessed.

Aquifers in Colorado are usually one of three types:

Alluvial Aquifers

Alluvial aquifers are generally shallow sand and gravel deposits laid down over time in a river channel or floodplain. The name “alluvial” refers to the loose, unlayered nature of the material – often silt, clay, sand, and gravel, deposited by running water in and around rivers.

Alluvial aquifers are often referred to as “tributary aquifers,” meaning that they exchange water back and forth with surface streams. Major alluvial aquifers surround every large river in the state, and smaller alluvial aquifers surround all the creeks and streams.

Colorado’s alluvial aquifers can supply water to cities and farms, but unless they are managed carefully, they can be over-pumped and/or polluted. If wells pump more water than is returned to an alluvial aquifer, this may mean less water is available in nearby lakes and rivers.

Sedimentary Bedrock Aquifers

Sedimentary aquifers exist deep under ground, primarily in sandstones and limestones. Multiple geological layers and aquifers exist at different depths. Examples of sedimentary aquifers in Colorado include the Denver Basin, High Plains, and Piceance Basin in northwestern Colorado.

These deep aquifers are often confined – rock layers above them have low permeability, which limit the amount of water that can move back and forth to the aquifer. These aquifers are typically not connected to nearby rivers, as alluvial aquifers are, so their groundwater is usually considered non-tributary. Deep aquifers still have recharge areas, but these may be many miles from the aquifer itself. Recharge for deep aquifers requires very long time periods – potentially thousands of years.

Fractured Rock Aquifers

Fractured rock aquifers are common in the mountains. Underneath a layer of soil and loose rocky material, aquifers exist in bedrock full of cracks and fractures created by the natural folding and faulting of the rock over millions of years. These cracks can fill with water supplied by infiltrating snow and rain. Not all fractures contain water, however. Springs can arise where fractures intersect the land’s surface.

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