It’s National Groundwater Awareness Week! I’m taking the opportunity to share some groundwater online information resources that I like.

Ever wish you could easily and quickly find the major regional aquifers at a location? Do you know what principal aquifers are in your area? Explore the The National Atlas Principal Aquifers Map. This interactive online map displays the outcrops of the principal aquifers of the lower 48 states plus Hawaii, the U.S. Virgin Islands, and Puerto Rico.

Principal Aquifers of the lower 48 States

If you’ve never used the map, here are some features to try:

  • Zoom out to the 50 states
  • Zoom in to a particular state
  • Search for a location name.
  • Click on the “map key” tab to display an explanation of the color and the name of the associated aquifer system.
  • Click on the “identify” button and then on a location within one of the aquifers to bring up a description of the principal aquifer at that location and links to additional information.
  • Email or save a map.
  • Select the “print” option to bring up a map image that is perfect to save for web use.
  • Explore the other layers in the map. Select multiple layers to display them at the same time. (Don’t forget to click on “redraw map” to have your changes display on the map.)

What is an aquifer?

An aquifer is a geologic formation, group of formations, or part of a formation that contains sufficient saturated, permeable material to yield significant quantities of water to wells and springs.

Does the map show all aquifers?

This map only displays the shallowest of the the major regional aquifers (principal aquifers) present at a location in the United States. The map does not display all aquifers present at a location or all the aquifers in the country. If you want to use the map for scientific purposes, you should take a look at the metadata for the details about what is and is not included.


Want to do more than explore online? You can buy a paper copy of the map, which is perfect for office and classroom displays. You can download the GIS files to use locally. If you would like more detail about the map, the metadata explains the data sources and how the map was compiled.

References and Resources

Basic ground-water hydrology (USGS Water-Supply Paper 2220)

Ground Water Atlas of the United States (USGS Hydrologic Atlas 730)

Principal Aquifers of the 48 Conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands (USGS)