By Richard J. Magill
One of the more important issues that green infrastructure professionals are discussing these days is responsible and effective re-use of stormwater in urban areas. Given the effects of global climate change (temperature inc2rease, rising oceans, extreme weather outbreaks- not the least of which includes devastating drought conditions), we are consequently experiencing profound increases in pollution of drinking water supplies, diminishing recreational-water opportunities, and the widespread degradation of our natural waterways and oceans, among other negative implications. Municipal, state, and federal programs in some parts of the world seem to be responding by promoting legislation that requires urban development projects to include measures to proactively manage and re-use this scarce resource. The proactive approach is particularly apparent in Western Europe, the United States, Canada, Australia, and New Zealand. Other parts of the world are just becoming aware of the possibilities and opportunities associated with wise re-use of this often neglected source of water.
For the purposes of this article, stormwater is defined as runoff collected from roof and ground surfaces, including roadways, driveways, parking lots, plazas, and other impervious areas. Rainwater is defined as runoff from roof surfaces or collection by other devices which don’t allow the rain to come in contact with imperious surfaces which collect pollutants.
The scale of stormwater harvesting and reuse systems can range from small residential systems to very large commercial systems. In the US, outdoor water uses represent 58 percent of the domestic daily water uses, while for hotels and office buildings, outdoor uses represent 10 to 38 percent of the daily water uses, respectively.
According to the U.S. EPA, when harvested rainwater is re-used, it generally is best suited for irrigation and non-potable uses, such as water closets, urinals and air conditioning systems (HVAC), as these uses require a lesser amount of on-site treatment than potable uses. Due to the lower cost of treatment, one of the most common re-use applications of stormwater and rainwater is for irrigation of urban green spaces. Some of the uses include irrigation of athletic fields, golf courses, parks, landscaping, community gardens, and even public water features. The green infrastructure techniques utilized to collect stormwater include bio-swales (rain gardens), enhanced tree pits, and permeable pavements. The following goals are central to the principles of stormwater harvesting and re-use systems:
- reduction of stormwater pollutant loads and flows to surface waters, helping achieve local stormwater management requirements;
- reduction in the size of other, more traditional stormwater management practices used to achieve local stormwater control requirements;
- reduction of the demand on potable water sources; and
- reduction of stress on the existing water supply and associated delivery infrastructure.
Well-planned, designed, and implemented stormwater harvesting and re-use systems can also be used to obtain valuable Leadership in Energy and Environmental Design (LEED) and other sustainable design credits related to stormwater quantity and quality, and water efficiency. LEED certification is recognized as a cost-effective (especially long-term) and environmentally-responsible practice, and is often embraced by the development community as a necessary initial cost of doing business, in the United States at least.
Concerns Related to Stormwater Harvesting and Re-use
Although stormwater harvesting and re-use systems appear are viable alternatives to help achieve required stormwater management standards, as well as reducing the demand on the potable water supply, they are not without significant concerns.
Those concerns include:
- Potable water supply cross-contamination;
- Direct human exposure to pathogens;
- Exposure to pathogens in food crops;
- Risk of toxic spills (within the stormwater re-use catchment area, and potential for re-use of contaminated water);
- Concerns with mosquito breeding; and
- Contaminated pond sediments.
Additionally, there are often not locally well-defined operation and maintenance procedures for rainwater and stormwater harvesting and re-use programs. These operation and maintenance programs help ensure stormwater re-use systems are functioning as designed and are meeting the required water quality standards to protect the public health.
Potential Obstacles to Progressive Stormwater Management Systems
In many areas of the world, rainwater and stormwater harvesting is largely unaddressed by regulations and codes. Many of the requirements that do exist were originally developed for the re-use of reclaimed water (treated wastewater) rather than stormwater. The confusion about the different types of water to be re-used (reclaimed, rainwater, stormwater, etc.) and the lack of legislative guidance for this topic has resulted in differing use and treatment guidelines and standards among federal, state and local governments. Because of the lack of guidance for rainwater and stormwater re-use, these sources of re-used water are often regulated at the same level as reclaimed water, which is typically more clearly defined by past management practices. Although the general guidance for the re-use of rainwater and stormwater is similar to reclaimed and grey-water, it can differ dramatically due to lower levels of initial contamination and the potential end-uses. Often, the treatment requirements ultimately come down to the risk of exposure to pathogens.
The perceived cost of improving stormwater management systems, relative to the actual long-term costs, is also an obstacle that needs to be overcome. The level of treatment required by each locality can influence the number of harvesting and re-use systems that are actually implemented. Simplifying the treatment requirements when public health is not at risk can lower the project cost for those entities intending to install stormwater harvesting and re-use systems and may encourage broader adoption of these improved practices.
What Can Green Infrastructure Professionals Do to Further the Cause?
While some governments may resist the codification of more progressive stormwater and re-use practices and regulations, green industry professionals can be leaders in the education and promotion of ideas that advance the stormwater management systems of developed and un-developed countries alike. The most effective means that landscape architects and designers, urban arborists and foresters, structural and civil engineers, and urban and regional planners can use to further the cause is knowledge. If we as professionals continue to pursue innovative, and environmentally and financially responsible practices, and educate citizens, supervisors, and elected officials on these newer management techniques, there can be substantial gains made against the negative effects of inefficient and outdated stormwater management systems in urbanized areas of our planet.
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