Drexel Study: Why Philly Should Use Rainwater to Flush Toilets

The economic and environmental benefits would be surprisingly big.


Purified water is wasted in toilet bowls, but flushing is the single largest source of water consumption in the U.S.

Some researchers at Drexel University have a better idea, one that would work particularly well in Philadelphia: use rainwater instead.

Franco Montalto and other Drexel researchers took a look at rainfall levels in big U.S. cities, and found that Philly is one of just four cities nationwide that gets enough rain to eliminate the need for tap water in the toilet. How? By using large storage bins to collect rainfall from rooftops then diverting that water to the bathroom whenever the need arises.

“There’s both an upstream and downstream impact,” said Montalto in a phone interview. Switching to rainwater on the “upstream” side would conserve drinkable water and reduce the strain on city watersheds, while on the “downstream” it would lower the amount of unwanted storm water runoff.

“When the natural landscape is replaced by a building, rain can no longer infiltrate into the ground,” said Montalto in an article for Drexel Now. “It runs off, is captured in drains, where it can cause downstream flooding, carry pollutants that settle out of the air into local water bodies or — in the case of a city like Philadelphia or New York — cause the sewer to overflow, which leads to a discharge of untreated wastewater into local streams and rivers.” They predict implementing the bins would reduce runoff by over 40 percent.

And the good news for residents is not only does the switch have positive environmental impacts, it’s also beneficial for your wallet. The study states that it could cut the water bill for an average-sized house by as much as one fourth. That’s about $17 a month, every month.

Montalto said implementing the program in a house is easiest when the house has downspouts. The process for houses with interior pipes is bit more complex but Montalto said he’s almost completed the process at his South Philly home. All he has left to do is put the pump in.