First Flush

The First Flush refers to the initial flow of water during the start of a rainstorm, especially after a dry period. This water often carries accumulated pollutants, dirt, oils, and debris from surfaces like roads, rooftops, and industrial areas. Because of this, the First Flush can significantly impact water quality in stormwater systems and receiving water bodies. Many stormwater management practices include "First Flush" control measures to capture or treat this initial runoff separately, helping to reduce pollution and protect environmental and public health.