Wastewater and Stormwater


Wastewater is made up of a community’s used water and solids (including water from industrial processes), and flows to a wastewater treatment plant. Treatment is needed before wastewater can be returned to the environment, to make it safe for wildlife and for human activities like fishing, swimming and drinking. Wastewater treatment techniques and technologies have advanced tremendously over the past century, keeping pace with population growth and changes in industrial processes, technological developments and land use. However, the basic function of wastewater treatment remains the same: to speed up the natural processes by which water purifies itself. In earlier years, the natural treatment process in streams and lakes was enough to treat our wastewater. As our population and industries have grown to their present sizes, increased levels of wastewater treatment have become necessary.

Most wastewater is transferred and treated through a system of pipes that lead to a wastewater treatment plant that is operated by a wastewater utility. Households that are outside of sewer service areas rely on decentralized systems, such as septic systems, to treat their wastewater. As of 2012, there are approximately 1.7 million onsite systems in operation throughout the Chesapeake Bay watershed. Both centralized and decentralized systems receive wastewater from a variety of sources, including toilet flushing, sink and shower drains, and washing machines.


Stormwater is precipitation in urban or suburban areas that does not evaporate or soak into the ground, but instead pools and travels downhill. Stormwater is also called urban stormwater, runoff and polluted runoff. Increased development across the watershed has made stormwater runoff the fastest growing source of pollution to the Chesapeake Bay and its rivers.

When it rains, water either runs off the land or filters into the ground. In urban and suburban areas, where roads, rooftops, parking lots and other impervious surfaces are common, most stormwater runs off the hardened surfaces and into local streams, storm drains and the Bay. As water runs across hardened surfaces, it picks up pollutants—including nutrients, sediment and toxic contaminants—which can harm aquatic life. Increased amounts of stormwater can also erode stream banks, degrade stream habitats and increase flooding in urban and suburban areas.

Development has increased stormwater runoff in the watershed:

  • Forests, wetlands and other naturally vegetated areas slow stormwater runoff and absorb water and pollutants. When these natural buffers are removed to make way for development, stormwater and the pollution it carries are able to flow freely into local waterways.
  • Impervious surfaces—roads, rooftops, parking lots and other hardened surfaces—do not allow precipitation to soak into the soil. Instead, water runs off and picks up dirt, trash, motor oil and other pollutants on its way to the nearest storm drain.
  • Muddy runoff from construction of new development contributes substantial amounts of sediment to the Bay and its tributaries.