Down the Drain
A new study suggests that city residents could be letting the benefits of an ubiquitous natural resource go to waste, when it could be used to reduce their water bills.

_Franco Montalto

Montalto is an associate professor of civil engineering, with research interests in the effects of built infrastructure on societal water needs, green design and more.

Good news for residents of Philadelphia, New York, Seattle and Chicago: It rains so much in these cities that if residents collected and stored the rain falling on their roofs, they could significantly reduce their water consumption, according to research by a team of Drexel environmental engineers.


An average residence with a 1,000-gallon rainwater harvesting system could reduce runoff by over 40 percent, according to the study.

_Less Runoff

This chart shows what impact 100 percent adoption of rainwater harvesting systems could have on citywide reductions in roof runoff from residential buildings.

Toilet flushing is the biggest use of water in households in the United States. But there is no reason that clean, treated, municipal water needs to be used to flush a toilet when rainwater is plentiful. Significant reductions in potable water used to flush toilets in residential buildings in four major cities could be achieved if rainwater harvesting systems were adopted in 100 percent of the cities’ residential buildings.

“People have been catching and using rainwater for ages, but it’s only been in the last 20 to 30 years that we have realized that this is something that could be done systematically in certain urban areas to ease all different kinds of stresses on watersheds; potable water treatment and distribution systems; and urban drainage infrastructure,” says team leader Franco Montalto, who is an associate professor in the College of Engineering and director of the college’s Sustainable Water Resource Engineering Lab.

The study was recently published in the journal Resources, Conservation and Recycling, and is one of the first to show how feasible, and beneficial, rainwater catchment would be.

Toilet flushing is the biggest use of water in households in the United States, accounting for nearly one-third of potable water use.With a 1,000-gallon storage tank, a three-person family with an average roof size would have enough water to cover over 80 percent of its flushes.