Public Water Supply: Designated Uses


Under the Clean Water Act (CWA), determining “Designated Uses” is typically the starting point for protection of any surface water, whether stream, river, lake, or pond. The CWA Water Quality Standards (WQS) program requires states and tribes to specify how each waterbody is used (e.g. ship channel, fresh water fishery, primary contact water, source of drinking water) and the water quality criteria necessary to protect those uses (e.g., 1300 ug/L copper). Once established, designated uses and water quality criteria provide the basis for further management actions under the CWA such as pollution permits (NPDES), enforcement actions, attainment decisions, and Total Maximum Daily Loads (TMDLs).

How can I use designated uses to protect drinking water sources?

States and tribes have discretion in determining whether or not to designate water bodies for public water supply and how to articulate such a use in their WQS. States and tribes may choose to apply a “blanket designation” of public water supply use to all waters in their lands or to designate a public water supply use on a waterbody-by-waterbody basis.

Each designated use requires a certain level of water quality be met to achieve the use—some designated uses require more stringent water quality criteria while others less. A public drinking water source designated use requires water quality criteria that are sensitive to human consumption and therefore provide a high degree of protection to public health.

Public drinking water sources are not always specifically designated and therefore do not receive the proper protections necessary to ensure safe sources of drinking water. When opportunities arise, stakeholders should petition state water quality directors to consider designating a public drinking water source for public water supply use under the CWA, if not so designated. States should also consider future drinking water needs (from population growth) so that water bodies can be designated and protected for future use. Come equipped with current information when approaching states: drinking water databases and national mapping tools like EPA’s Drinking Water Mapping Application to Protect Source Waters (DWMAPS) can be used to identify source waters that are not already designated for public drinking water supply use.

  • Encourage states to designate all public drinking water sources for “public water supply;” not all sources of drinking water may be designated as such
  • Come equipped with pertinent, current information

Opportunities for involvement

Once established, designated uses rarely change. However, the CWA requires states to review, revise (if appropriate), and adopt water quality standards every three years in a process called the Triennial Review of Water Quality Standards. States also perform “use attainability analyses” to consider changes to designations. Both processes are subject to public notice and opportunities for involvement. There are also opportunities to petition a state agency to revise a use. Find more information at your state environmental agency website, found here.

For more information on protecting drinking water through the Clean Water Act, see Opportunities to Protect Drinking Water and Advance Watershed Goals through the Clean Water Act: A Toolkit for State, Interstate, Tribal, and Federal Water Program Managers.