Profile: Sara Finley: Riding the greywater wave

Profile: Sara Finley: Riding the greywater wave McGill University

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McGill Reporter
March 20, 2008 - Volume 40 Number 14
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Sara Finley: Riding the greywater wave

Caption follows
Sarah Finley says that elsewhere in the world, greywater is being considered for such water-intensive activities as firefighting and industrial car-washing.
Owen Egan

In the fall of 2004, while working for an NGO in Senegal, International Studies grad Sara Finley had a professional epiphany. Some might call it a rude awakening.

Finley was in the capital, Dakar, trying to design and implement effective urban agriculture initiatives for residents of the city, many of whom were impoverished. At a Methodist church where a successful rooftop garden project was in full harvest, Finley was hoping to teach a group of residents about the benefits of small-scale urban agriculture.

"Your garden is very, very pretty," one local smiled, "but we have no water."

Finley was floored. "I was coming from Canada and working for an NGO that was paying the water bills," she remembers. "I hadn't calculated that in my design."

A year later, the experience dovetailed nicely when Finley began working with a green architect who was interested in greywater – the domestic wastewater stream that excludes "black water" from toilets, dishwashers or kitchen sinks. Significantly less polluted than black water, greywater is gaining currency worldwide as a viable source of irrigation water – especially in areas hit hard by drought.

Finley's curiosity was more than just a little piqued. So much so that she enrolled as a Master's student in Bioresource Engineering so, in her own words "I could learn about the chemistry and microbiology of greywater."

Last year, Finley devised a greywater research project for her thesis in collaboration with a friend who had installed a greywater-treatment system in the basement of his Park Ave. home and was determined to use the recycled water in his edible rooftop garden. Finlley decided to replicate his garden under laboratory settings and measure what effects, if any, greywater would have on crops.

Not surprisingly, little of the information she gleaned came from Canada, where our misconception of being able to tap into an unlimited supply of fresh water has turned us into water snobs – turning our noses up at any water that isn't absolutely pristine. "There's lots of conflicting information out there, most of it anecdotal," Finley said of the safety of using greywater on edible plants. "Some people say 'It's great, I feed my whole family with crops watered with greywater,' while others say 'It's full of bacteria. You'll die! You'll die!'"

Finley planted three types of vegetables; those that grew below the soil (carrots); those that grew on top of the soil (lettuce); and those that grew above the soil (peppers). She also used two batches of water: one from the test subject's greywater-treatment system and one of tap water as her control, making sure the water went directly to the soil and was never sprayed onto the plants.

Following the natural growing cycle, Finley's project ran from May to October, the last eight weeks of which were devoted to testing and analyzing her crops.

Measuring the water for everything from heavy metals and ph levels to grit and bacteria, Finley noticed the levels of fecal bacteria were high in the greywater, although "not higher than what I found in the literature," she said. That said, she was able to characterize the greywater as low- to medium-grade wastewater very similar in quality to that which is dumped back into the St. Lawrence after treatment.

What did surprise Finley, however, was how relatively unaffected the vegetables were by the regular contact with the greywater. "Even though the water was quite polluted, there wasn't an obvious effect on the crops," said Finley. "I was expecting something because my control was tap water which has no bacteria and two batches of greywater which had from 10,000 to 100,000 bacteria per 100 millilitres – which is a lot. Overall there was no significant trend."

Her findings showed fecal coliform bacteria were more present on the surface of carrots, less on lettuce and none at all on peppers – which makes sense, considering their length of contact with the greywater. Still, none was so high that she considered it dangerous. "You wash the vegetables before you eat them, and that will remove some of the bacteria. If you are really in doubt, you boil them or steam them."

Eat them? That's right, like the best budding young researchers, Finley didn't hesitate to put her mouth where her money was, sampling her harvest with no ill effects. The owner of the house has gone a step further, using his bumper crop to make everything from pesto to spaghetti sauce. "He's doing fine, too," Finley said, smiling.

When asked about the risks involved in introducing greywater into the earth through our gardens, Finley is quick to point out that soil is a vastly superior filtration unit than the crumbling, out-dated systems employed in most urban centres. "As long as you don't inundate the ground with tons of wastewater, or include things that won't break down, like PCBs, the earth will generally take care of the rest," she said.

Although Canada is a long way from widespread greywater use like that found in such parched places as Australia, there is increasing interest in the Prairie provinces, where water shortages and droughts have wreaked havoc with the farming industry.

And while Finley is the first to admit there are a number of obstacles to be overcome before Canadians start riding the greywater wave, there is a great benefit to be had even above the conservation of water. "You have a consciousness of what you put into your waste. You say 'this is what I put into my water and it's going to end up in my environment.' It wakes you up."

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