Q: Rain barrels are commonly used to collect rainfall for use in watering ornamentals. What are your thoughts and concerns about using gutters and downspouts to catch rainwater in stock tanks with the goal of watering horses?
A: It is not recommend to use rain barrel water for human or pet consumption, or even for watering root crops and vegetables that will be consumed. There are potential issues with runoff from rooftops in terms of safe drinking water.
Atmospheric deposition of fine metals and particulates can be carried into roof runoff and possibly concentrated in the rain barrel water, as can petro-chemicals from shingles. New roofs can be especially prone to releasing particulates and chemicals into runoff, particularly when there hasn't been much rainfall for a while and the sun has been heating the rooftop.
In a setting where there may be birds roosting or resting on the rooftop, you can also get significant amounts of bird droppings in the runoff, and that can contain salmonella and other bacteria that can be potentially pathogenic (disease-causing).
By Barb Liukkonen, Water Resources Center, University of Minnesota