In a recent article about rain barrels, I made the statement: “Water collected in a rain barrel is not suitable for vegetable gardens, human, or pet consumption as it may contain contaminants such as zinc, lead, chromium, arsenic, polyaromatic hydrocarbons, fecal coliform, and E. coli.” Several readers contacted me for clarification as well as confirmation of my sources.
Each of those readers received a personal response. However, my assumption from the number of inquiries is that there are more people who are wondering about this information, but just haven’t asked.
Information sources
When researching the information for the rain barrel article, all University or Extension research-based sources were used, including Rutgers, Universities of Wisconsin, Minnesota, Kentucky, and Illinois. Rutgers, University of Wisconsin and University of Minnesota. They all specifically cautioned against using rain collected in rain barrels for human consumption or for watering vegetable gardens.
Facts about water collected from a roof
Water collected from a roof likely will contain at a minimum bird dropping and may well contain droppings from other creatures that have scampered across it. This is the source of the fecal coliform and E. coli contamination. In addition, bacteria and moss grow on cedar and asphalt roofs. Some asphalt shingles have zinc particles imbedded in them as moss preventatives. Zinc anti-moss strips also produce toxic chemicals that are unsuitable for use in a vegetable garden. Furthermore, if the roof has been treated with any type of moss, lichen, or algae killing chemicals in the past few years, the water collected would be deemed unsafe.
Asphalt shingles also contain various complex hydrocarbons that can leech into the water. Of course, a steel roof would not have this particular problem but certainly bacteria of some sort grows nearly everywhere!
How locations affect water quality
One other consideration is location. For example, air pollutants from a home directly under the flight path of an airport might contain heavy metals that wash off. Air pollutants from manufacturing sites, agricultural fertilizer residue, controlled burns of wildlife areas and other sources all settle on a roof only to be washed into the rain barrel.
The most highly contaminated water will be that “first flush” of rain after a dry spell. There has not been a great deal of testing done regarding the exact level of contamination. Therefore, most sources choose to err on the side of caution. Some research indicates that it is not a significant amount, while other research suggests that in at least some plants, there is recordable uptake of contaminates from the soil.
It is possible to have water from your rain barrel tested. This isn’t necessarily a practical solution as the contamination can vary from rainfall to rainfall. If you chose to take the risk and use the water on your vegetables, avoid overhead sprinkling onto the edible portion of the plant. Direct the water at the base of the plant and try not to use it close to harvest time. This will prevent contamination of the edible portion of the vegetable. In addition, always thoroughly wash produce regardless of the growing method with clean water before consumption.
Benefits of harvesting rain water
Rain barrels are a wise investment. Harvesting rain water has many benefits including saving water, saving money on your bill, and being a wise steward of resources. The water collected can safely be used for watering lawns and ornamentals. It can also be used for washing your car and your muddy feet! Just use it with caution around anything intended for human consumption.
Carol Shirk
Certified Master Gardener