Green Buildings and Water Infrastructure

As engineers, city planners, and others in the construction industry build more environmentally friendly buildings, adequate water infrastructure is becoming an important consideration.

Published July 1, 2006

By Franco Montalto and Patricia Culligan
Academy Contributors

The population of New York City is expected to rise by one million people over the next two decades. How will the city’s aging sewer infrastructure keep up?

The Leadership in Energy and Environmental Design (LEED) Green Building Rating System has been a good first step in encouraging green building practices. LEED provides credits for meeting specific requirements associated with sustainable site development, including water conservation.

But this initiative focuses primarily on building performance and not on the constraints implied by local water infrastructure. There is the real possibility that a building that has earned LEED credits for water use reduction could contribute more wastewater to the combined sewer system (CSS) than the structure it replaced, especially if the new building has higher occupancy and/or a larger footprint. Hence, even green buildings can increase the need for, and cost of, water infrastructure.

This is not the case for 7 World Trade Center, which will have a lower occupancy and smaller footprint than the building it replaced.

Minimizing Water Consumed and Wastewater Discharged

But we need to be thinking of new ways to optimize individual, or collective, site designs to minimize the water consumed and the wastewater discharged. This requires the optimization of all possibilities onsite, and may also involve the incorporation of offsite solutions within an appropriate service area.

Imagine a situation, for example, where all onsite opportunities for water conservation and reuse have been exhausted, yet there is still a net increase in load to the CSS at a development. This net increase would ordinarily result in an increase in sewer overflows.

Mitigation for the net increase could be implemented off site at distributed locations, all located within the local sewershed. Specifically, water conservation and stormwater-capture measures subsidized by the developer could be used to reduce flows in the sewer system in proportion to the net increase in flows resulting from the development itself. Such a plan would be the water infrastructure analog to the emissions trading program outlined in the International Kyoto Protocol, or the compensatory wetland mitigation program described in Section 404 of the Federal Clean Water Act.

Mitigation strategies could include water conservation measures, as well as neighborhood rainwater harvesting and reuse schemes, green roofs, and curbside infiltration galleries, all of which would reduce the total volume and rate of flow to the local CSS infrastructure. Considered in this context, even new developments of large scale could result in a net zero or even a reduction in the number of sewer overflows in local surface water bodies.

Green urban development requires new, comprehensive models and guidelines regarding how development and redevelopment projects relate to local water infrastructure capacity. Current development in New York City, including development at the World Trade Center site, provides the opportunity for leadership in achieving this goal.

Also read: Tales in New Urban Sustainability