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Water Use in the United States

Water-Resources Region Descriptions

Hierarchy of water-resources regions

Hierarchy of water-resource regions

The United States is divided and subdivided into successively smaller water-resource regions (areas), as shown in the above diagram. The regions are arranged within each other, starting from the smallest (water-resources cataloging units) to the largest (water-resources regions). All areas have unique numbers to identify them. Two digits specify each individual area, and the numbers are progressively appended to specify the more detailed areas, as shown in the examples below:

Water-Resources Region:  04 
Water-Resources Subregion:  0403 
Water-Resources Accounting Unit:  040302 
Water-Resources Cataloging Unit:  04030201 

Thus, region 04 includes a number of subregions, one of which is 0403. Subregion 0403 includes a number of accounting units, one of which is 040302. Accounting unit 040302 includes a number of cataloging units, one of which is 04030201.

In some of the water-use files and documentation you may see some alternate terminology. Here's how the terms relate:

Region: 2-digit hydrologic unit
Subregion: 4-digit hydrologic unit
Accounting Unit: 6-digit hydrologic unit
Cataloging Unit: 8-digit hydrologic unit

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