Sewer overflows happen when systems are overwhelmed, usually during rainstorms or when power outages cause pollution holding tanks to fail. Overflows are especially troubling and hazardous in areas where municipal and septic waste are sewered together. In these "combined sewer" areas, such as Washington, DC, rainstorms can cause vast amounts of unprocessed human waste to enter our water supply.

The results are catastrophic. Bacteria from unprocessed sewage poses many threats to human and environmental health. Biological pollutants like nitrogen and phosphorus give rise to algae blooms that suffocate aquatic life and bacteria that can irritate your skin. Some man-made pollutants, including a class of chemicals called endocrine disruptors, slip through the screening process undetected and end up in our drinking water.

You can learn more about sewer overflows on our blog.