Groundwater use in Colorado dates back to before the turn of the 20th century. Nineteen of Colorado’s 63 counties rely solely on ground water for potable supplies and domestic uses. Groundwater withdrawals by private wells and public water supply systems serve an estimated twenty percent of the state’s population. Agriculture is the largest user of groundwater, primarily for irrigation. However, groundwater is also used to meet nearly all livestock and rural domestic water needs.

Groundwater is simply water that occupies the pore spaces or crevices or fractures within soil or rock. Some materials have a greater ability to store and transmit water than others. An aquifer is a groundwater reservoir composed of geologic units that are saturated with water and sufficiently permeable to yield water in a usable quantity to wells and springs. Sand and gravel deposits, sandstone, limestone, and fractured crystalline rocks are examples of geologic units that form aquifers. The USGS identifies seven principal aquifers or aquifer systems in Colorado: South Platte Aquifer, Arkansas Aquifer, High Plains Aquifer, San Luis Valley Aquifer System, Denver Basin Aquifer System, Piceance Creek Basin Aquifer, and the Leadville Limestone Aquifer of west-central Colorado.

Sufficient water for a single household may be relatively easily obtained from wells in the bedrock aquifers, even the crystalline Precambrian rocks of the mountains. However, as households multiply, creating increased demands from many wells, a local aquifer with very limited storage that was sufficient for a few users, may be quickly depleted or polluted. Through wise water-management policies, protective regulations, and conservation activities, we can assure both the availability and the suitability of groundwater for future use.

The recently published ON-010 Colorado Groundwater Atlas has detailed information about every aspect of groundwater across the state. The CGS is also continuing its program of reporting on the groundwater resource status of individual counties across the state.