Praxis (Building Solutions)

Strive to Operate within Site's Natural Water Budget

1 of Green Village Philadelphia's Performance Goals

By Max Zahniser and Terrie Lewine

Orginally published in the Green Village Philadelphia Newsletter

A site’s Natural Water Budget is our term for water that can be collected from rainwater or the underground aquifer within the boundaries of the site.

The intent of Green Village Philadelphia with regard to this performance goal is to eliminate our negative impact on natural surface and ground water, as well as energy use related to municipally supplied water, while limiting but meeting our needs for water use.  Our design plans to reduce storm water runoff, infiltrate more rainwater and to have a positive effect on the aquifer.  .

In a natural state, rainwater lands on the surface of the earth, infiltrating and recharging the aquifer, with some runoff into the rivers and streams.   In cities, we are basically ignoring the water that is falling on us, and because we have radically decreased the permeability of the earth in these areas, almost all of the rainwater is flowing directly into stormwater systems, which bypass the aquifers.  By ignoring the rainfall we become dependent on municipally supplied water to meet all of our needs, although in some areas wells are common also.  Municipally supplied water is generally collected from surface water bodies like rivers and lakes, impacting those habitat systems, and is then treated using processes which are energy and chemical intensive.  Moving the water throughout the city is also highly energy intensive, so addressing water source and use also helps us to address another of our performance goals: Strive to operate within site’s renewable energy budget.

Our plan is to collect rainwater, store it, treat it as necessary, use it (to the extent we are allowed to by law) and finally let it recharge the aquifer as it would in a natural state. This will reduce our demand on municipally supplied water, and begin positively impacting the aquifer. 

In general, rainwater is not considered potable by municipalities.  Which means we can use it for waste water conveyance (flushing toilets, for example), and irrigation, but not many other indoor uses.  The possible uses of collected and treated rainwater is an example of policy advances Green Village Philadelphia might influence as a demonstration project.

These current building code limitations might drive us to draw upon well-water for some uses, but our concern will continue to be to return the water to the aquifer after use and treatment. In conjunction with rainwater use, limited well-water treatment and use may enable us to eliminate our municipally supplied water demand.

There are living-systems approaches to water treatment that can be quite attractive, and which GVP intends to integrate into the community. Two examples of this are Living Machines (usually indoor) and Constructed Treatment Wetlands (outdoor).  Tiny organisms that live in the root structures of the plants in these systems destroy the bacteria in our “waste”, providing clean water that can be returned to the aquifer or used again—which generally is not yet allowed by building code.  These living-systems use natural ecosystem processes and are energy efficient. 

We believe Green Village Philadelphia can approach achieving this performance goal by using a balanced combination of the strategies discussed above.

 

A technical sustainability consulting company with clients and strategic partners including University of Pennsylvania, the Pentagon, B Lab, the U.S. Green Building Council, Autodesk, Con Edison Company of New York, Wallace Roberts & Todd, Humanscale.