Copper Roofs and Water Runoff - An Overview

This report is based on research and progress addressing concern that copper released from copper roofs enters the groundwater, rivers, lakes and causes harm to fish and other aquatic organisms.

Most metals are of natural origin and a fundamental component of the earth's crust. Copper is no exception, and in addition, is essential to the health of all living organisms. All life forms have a requirement for copper. The essential question is not whether copper is toxic but whether the copper runoff from roofs can increase concentration of copper in lakes, streams and groundwater to such high levels as to become a hazard.

Newly installed copper roofs immediately begin to weather and oxidize. This weathering process actually produces a self protective coating on the copper called a patina. This is the blue/green color associated with copper roofs. It is complex, very durable and extremely stable.

It is the chemistry of the atmosphere and particularly of dew, especially its degree of acidity, that determines if any of the patina surface is dissolved. Rain simply provides the vehicle for transporting the dew and its contained copper products from the roof. This is the potential mechanism by which copper can be released from the surface of the patina and transported. Because the copper salts that form the surface layer are very insoluble, only very low levels of copper occur in the dew. The concentration of copper salts is highest in the first few liters of runoff, the "first flush".

Research completed in 1999 at the University of Connecticut shows that the ionic copper, which is potentially harmful, is rapidly transformed into a benign, non-bioavailable form because of its interaction with drainage components. Therefore, the copper no longer presents any threat the environment.