Net Zero Water is an up-and-coming sustainable building concept that is analogous to the better-known Net Zero Energy. The goal of Net Zero water is to achieve water independence and manage most—or ideally all—stormwater runoff. Green roofs are one of the most powerful tools to accomplish this, especially on a large scale.

Studies have shown that a traditional roof’s runoff contains high concentrations of pollutants from rainwater, roofing materials, and atmospheric deposition. Storm water and sewage systems also involve high capital investment into the components, continual maintenance and inspection.

By capturing and temporarily storing storm water green roofs can reduce run-off volumes. The plants and growing media used in green roofs help decontaminate run-off, loading fewer pollutants into the municipal storm water system. By increasing stormwater retention, green roofs can also reduce the need to expand or rebuild related infrastructure.

Many older cities have combined sanitary and storm sewers, whose treatment capacity can be overwhelmed by heavy precipitation. By capturing and temporarily storing storm water, green roofs can reduce run-off volumes. By reducing runoff, green roofs can limit the occurrence of combined sewer overflow (CSO) events and thereby diminish the quantity of untreated wastewater entering fresh water bodies. By reducing peak flows during storm events, green roofs can reduce the incidence of flooding.

Due to the reduced quantity of storm water run-off, smaller roof drains may be possible on a green roof. Storm water and sewage systems involve high capital investment into the components, continual maintenance and inspection. A 2005 study by the Casey Trees Endowment Fund, Re-greening Washington, DC: a Green Roof Vision Based on Quantifying Storm Water and Air Quality Benefits showed that a green roof can retain between 65-85% of stormwater runoff compared to a conventional roof, depending on whether the green roof is extensive or intensive.  The excess storm water can also be collected on the roof or at grade in a cistern and used later to irrigate the vegetated areas, reducing the use of potable water.

Green roofs also improve storm water run-off quality. The plants and growing media used in green roofs help decontaminate run-off, loading fewer pollutants into the municipal storm water system.

Increasingly, jurisdictions have begun to implement Storm Water Utility Fee charges, which help raise capital for improved storm water management. The fees assessed to each property owner are typically based on the impervious surface area of the property. For commercial and industrial buildings, the large amount of impervious surfaces often results in larger new storm water fees, which can be a significant cost over a twenty to forty year period. Storm water fee rebates or reductions can provide a monetary incentive for the use of best management practices.

Green Roofs for Healthy Cities has developed the Introduction to Integrated Water Management with the American Society of Irrigation Consultants (ASIC) committee members, to leverage additional government and public awareness by providing technical and economic information on the design and performance of a fully integrated site and building water management system based on the “Net Zero Water” concept.

This approach promises to significantly reduce the consumption of potable water in buildings, reduce discharge to municipal waste water system and save on municipal energy by reducing the amount of potable water treated at municipal facilities. At the same time the Net Zero Water concept will develop and efficiently manage limited water resources in order to deliver truly sustainable living systems to the urban environment.  Recognition of the connection between water management and energy conservation is emerging as a new opportunity in integrated management systems.

The Introduction to Integrated Water Management course will be delivered at the 8^th Annual CitiesAlive Green Roof and Wall Conference in Vancouver BC, November 30 – December 3. The course will soon also be available online on the Green Roofs for Healthy Cities’ website as one of many educational seminars and courses on the Living Architecture Academy.

This Introduction to Integrated Water Management course can be used as continuing education credits for the Green Roof Professional (GRP) accreditation designation. Launched in 2009, the GRP accreditation is supported by four professional development courses offered in different locations throughout North America.  The importance of water conservation is only going to increase in the near future and professionals will be needed to respond to this demand. The GRP program is a unique learning opportunity for landscaping and irrigation practitioners to get involved in the sustainable construction industry.

About the Authors
Steven W. Peck, GRP, HASLA is the founder and president of Green Roofs for Healthy Cities, the North American Industry Association for the green roof and wall industry.   Damon van der Linde is the Communications and Research Coordinator at Green Roofs for Healthy Cities. www.greenroofs.org