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Potential Contaminants in Residential Rain Barrel Water

Potential Contaminants in Residential Rain Barrel Water

FS280E
Dr. Linda Chalker-Scott, Extension Urban Horticulturist and Associate Professor, Washington State University
Home gardeners often collect rainwater to supplement summer irrigation, but rooftop runoff can be contaminated. This publication examines the research behind residential rain barrel water safety in and provide science-based suggestions for using rain barrel water in ways that protect people, pets, and the environment.
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Residential gardeners often collect rainwater to supplement summer irrigation. They may also use rainwater as an unchlorinated water source for aquatic plants and animals. However, rooftop runoff can be contaminated with chemical and biological pollutants. This publication will examine the research behind residential rain barrel water safety in North America over the last 20 years. It will also provide science-based suggestions for using rain barrel water in ways that protect people, pets, and the environment.

Rain Barrel Practicality

Rain barrels can help reduce the use of relatively expensive, treated water for nonpotable applications such as watering garden and landscape plants. Alternative sources of nonpotable water are increasingly important in chronically or seasonally arid parts of the country. Rain barrels (Figure 1) are relatively inexpensive to obtain and install, and residential costs are typically recovered within 3–6 years of installation (Logan 2014).

Figure 1. Typical garden rain barrel installation. Photograph courtesy of William McCabe
Figure 1. Typical garden rain barrel installation. Photograph courtesy of William McCaleb.

Rooftop collected rainwater has been tested on container plants as well as those planted into gardens and landscapes. In all cases good results have been seen, with no plant disease or disorder problems apparent (Chen et al. 2003; Islam et al. 2013). But rain barrel water is untreated and unregulated. There are legitimate safety concerns about exposure of people, pets, and the environment to rain barrel water.

What Contaminants are Found in Rain Barrels?

Many studies have identified rain barrels as reservoirs for toxic materials and pathogenic microbes (Hart and White 2006; Lye 2009; Schuster et al. 2013). Possible rain barrel contaminants fall into two general categories: biological and chemical.

Biological Contaminants

  • Bacteria
  • Cyanobacteria
  • Fungi
  • Protozoa

Chemical Contaminants

  • Metals, especially heavy metals
  • Nutrients
  • Particulates (adsorb other chemical contaminants)
  • Pesticide residues

Researchers have looked at nutrient loads, heavy metal content, pesticide residues, and microbial contaminants in rainwater collection systems in hundreds of studies from all over the world (Table 1). In North America, the main concerns are fecal contaminants and heavy metals.

Table 1. Contaminants identified in international rainwater collection studies from 1996–2016.
Table 1. Contaminants identified in international rainwater collection studies from 1996–2016.

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