designated use

Per the Clean Water Act, a designated use for a waterbody is a use specified in water quality standards for each segment of the waterbody, such as swimming, fishing, drinking water or irrigation, regardless of whether that use is being attained or not.  “Waste transport” is not an acceptable designated use.  Designated uses are set by the state or tribe that has responsibility for the waterbody and are central to establishing water quality standards.  Designated uses articulate a vision and establish water quality management goals for the waterbody, and also serve as the basis for discharge permits.

For more on designated uses: http://water.epa.gov/scitech/swguidance/standards/uses.cfm