Expert: Randy Johnson - 7/17/2007

Question
We are installing a rainwater collection system from our new asphalt roof.  We intended to use this water for our landscaping, greenhouse and vegetable garden.  We had heard, however that there were contaminants in water collected from asphalt shingles.  Please give me any info you may have relating to this.

Answer
Hello Jan -

Rainwater collection seems to be a popular topic. I have had several people ask the same question recently.

I checked with several plant scientists, and the answer was that there should not be any problems with vegetables watered with normal run off from a normal asphalt roof.  The amounts of any petroleum contaminants would be small, and plant roots are not designed to take up petroleum products.

I would add, particularly with a new roof, that you may want to install a bypass system that dumps the first few gallons from a rain away from the cistern.  Much of the contamination (both from the asphalt, bird/animal droppings, and other sources, can be discarded in this manner.  

Best wishes.

Randy