Down the drain: Here's why we should use rainwater to flush toilets

http://www.eurekalert.org/pub_releases/2016-03/du-dtd030716.php

Public Release: 7-Mar-2016
Down the drain: Here's why we should use rainwater to flush toilets
Drexel research looks at feasibility of rainwater recycling in 4 major US cities
Drexel University

If you live in one of four major U.S. cities chances are you're letting the benefits of a ubiquitous natural resource go right down the drain -- when it could be used to cut down your water bill. Research by a team of Drexel University environmental engineers indicates that it rains enough in Philadelphia, New York, Seattle and Chicago that if homeowners had a way to collect and store even just the rain falling on their roofs, they could flush their toilets often without having to use a drop of municipal water.

Toilet flushing is the biggest use of water in households in the United States and the United Kingdom, accounting for nearly one-third of potable water use. But there is no reason that clean, treated, municipal water needs to be used to flush a toilet -- rainwater could do the job just as well.

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"When the natural landscape is replaced by a building, rain can no longer infiltrate into the ground," Montalto said. "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. So capturing rainwater can help to reduce the demands on the water treatment system and ensure that it will still function properly even during heavy rainfall events."

Taking into consideration the cities' annual rainfall patterns, residential population and roof areas, the team calculated that, with enough water storage capacity -- a little more than a standard 1,000-gallon home storage tank -- a three person family in a home with the city's average roof size would have enough water to cover over 80 percent of its flushes throughout the year simply by diverting their downspouts to collect stormwater.

This would reduce overall household potable water demand by approximately 25 percent, which could mean slashing the municipal water bill for an average-sized home by as much as one-fourth. But even without installing a storage tank capable of holding a year's worth of flushing water, a scaled-back version would still help chip away at the water bill.

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"Think of it this way. Before the building was on the site, the rain was intercepted by vegetation canopies, and/or infiltrated into natural soils. Either way, the rain ended up replenishing soil moisture, allowing the plants to grow, and recharging the local groundwater aquifer," Montalto said. "The more buildings that go up, the more we need to consider how to manage the water that would have landed in the drainage area they're displacing."