Protecting the Most Sensitive Uses

The regulations require that designated uses must protect the most sensitive uses in the water. Many people assume that “Swimming” is a more protective designation than “Aquatic Life” and that “Drinking Water” is more protective than “Swimming.” Thus, they assume that if their waterbody is designated as “Drinking Water,” it is receiving the strongest possible protection.

But the relative stringency of designations can only be judged on a pollutant-by pollutant and use-by-use basis. For example, increased salinity does not harm a swimming use (after all, people do swim in the ocean), but it could be disastrous for some freshwater fish and many of their food sources. Moreover, increased bacteria in a water body may not create an immediate hazard for people in cities that use it as a drinking water source (because bacteria, up to a point, can be treated in a drinking water treatment plant), but it could put people who swim in the water body at immediate risk. It is important to note that in protecting drinking water as a use, the Clean Water Act protections assume at least the basic required treatment will occur.

So, a “Drinking Water” designation is not necessarily more protective than a “Swimming” designation, and a “Swimming” designation is not necessarily more protective than an “Aquatic life” designation. This is why multiple designated uses are often necessary to protect all existing uses.

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