Use of Roof Water Run-Off

Technical Bulletin #28

Current as of May 2019

In some regions, homeowners may want to use their roof water run-off from rain for various domestic/household purposes. While asphalt shingles are considered safe in terms of groundwater and leachate contamination (they do not contain heavy metals or toxic chemicals based on groundwater leachate testing), all roofs, regardless of materials used, collect environmental contaminants that may render the water run-off unfit for human consumption. For example, wind-blown dirt and dust, insects, certain plant and algae species, bird guano as well as waste from raccoons and other rodents come to rest on roof surfaces. Subsequent rains dissolve these materials to varying degrees, washing them down gutters and downspouts into barrels, collectors or cisterns.

Typically roof water run-off without additional treatment is suitable for watering plants, shrubs/trees, lawns, etc.  However, use for direct or indirect human needs, such as cooking, drinking, or washing, will require filtering, sanitizing equipment/chemicals to cleanse the naturally occurring contaminants described above.

Historically cisterns have been successfully used in conjunction with homes roofed with asphalt shingles. However, CASMA has no expertise in determining water potability and sanitizing processes.  

CASMA recommends that homeowners who wish to use rain water from their roofs should contact their local water supply and health officials to determine what safety standards, testing procedures and treatments would apply.

The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.