As a kid, I always loved field trips. You not only got to leave school and take a bus ride, you also got to visit exotic places like dairy farms, museums and newspapers.
One field trip that seemed to be repeated at regular intervals during my school years was to the local water treatment facility. I always enjoyed those trips, not only because of the school-leaving and bus-riding, but also because I’d seen the lake our drinking water came out of in Weyburn and it was a great relief to know how thoroughly it was cleaned before it made it to our taps.
A lot of towns in Saskatchewan draw their water from relatively shallow prairie lakes like Weyburn’s Nickle Lake, or Regina and Moose Jaw’s Buffalo Pound (an unfortunate name for a drinking-water reservoir, I’ve always thought). Scoop up a glassful of brown and/or green water from one of these lakes in the middle of the summer, and it you didn’t know better, you’d swear there was no way that water could ever be made drinkable.
But, fortunately, there is a way. In fact, there are a lot of ways, some of them ancient. Sanskrit writings from 2,000 BC speak of purifying water through boiling in copper vessels, exposure to sunlight, filtering through charcoal and cooling in earthen vessels. However, water purification wasn’t applied on a city-sized scale until the 19th century, when people began to realize that epidemics of cholera and other diseases were related to the contamination of drinking water. (Cholera killed 14,600 people in London in 1848, and 10,675 in 1854. More than 50,000 people died in the U.S. from typhoid fever due to contaminated water between 1900 and 1904.) These epidemics would have been even worse if some cities hadn’t been fortunate enough to have sources of drinking water that required no treatment.
Some European cities had water filtration systems as early as 1829, but more than filtration was needed to stop the spread of disease. That required a way to disinfect the water, and that arrived in 1908, when chlorine compounds were first added to city water supplies in the U.S. Chlorine gas replaced the solid compounds for municipal water treatment in 1911. By the 1930s, waterborne diseases were largely eliminated in North American cities.
Today, each city uses a different selection of water treatments, depending on the quality of water it begins with (and the amount of taxpayers’ money available). To learn about the procedures used at the Buffalo Pound water treatment facility, I talked to Stan Baldry, a water technologist with the City of Regina. The path our drinking water takes from lake to tap goes something like this…
First, the water is chlorinated. This step isn’t used by a lot of cities; usually, chlorination is the last step in water treatment. Adding a few parts per million of chlorine to water kills dangerous bacteria, but the reason our water gets chlorine before any other treatment isn’t primarily to kill bacteria, but rather to kill algae, which thrives in shallow, sun-warmed lakes like Buffalo Pound.
The next step is coagulation: chemicals (primarily alum) are added to the water which cause fine particles to clump together. Powdered activated charcoal is also added: this absorbs taste and odor-causing compounds in the water.
Flocculation comes next–and no, flocculation isn’t something that the film classification board objected to in Exit to Eden. It’s a gentle agitation that makes the coagulated particles from the previous stage of treatment clump together into even larger, heavier bits.
Next comes “upflow clarification,” a slow upward welling of water inside a large tank. This helps remove the coagulated particles from the water; they get left behind as the water moves upward.
The next step is filtration. One reason why well water (which Regina also uses to supplement the water supply) usually needs very little treatment (in Regina’s case, just chlorination) is that it has been extremely well filtered over long periods of time as it sinks down through the various levels of soil, sand, clay and rocks between the surface and the depth at which it finally collects. Filtration simply speeds up this natural water-cleansing process. At the Buffalo Pound plant, water is filtered through a “graded mixed media sand filter.” Basically, the water passes through progressively finer layers of sand, each layer trapping smaller and smaller particles.
From early spring to late fall, Buffalo Pound water also passes through Granulated Activated Carbon filters, GAC filters for short, the devices which, over the past few years, have managed to just about stamp out jokes about Regina’s bad-tasting water. (Which, by the way, I never thought could hold a candle, bad-taste-and-odor-wise, to the water out of Nickle Lake we drank in Weyburn during the drought years of the 1980s.) Carbon filtration works through a process called adsorption. There are many taste-and-odor-causing organic chemicals which can find their way into water which cannot be removed simply by passing the water through very fine sand. However, the molecules of these chemicals cling to the surface of the activated carbon. A small volume of granulated activated carbon presents a huge surface area, which allows a compact filter to remove enormous quantities of these chemicals.
After filtration, the water goes into the “clear tank” (co-called because, at this point, the water is, indeed, clear), and chlorine is added to bring levels up to those required by law. (Much of the original chlorine has been removed by other treatments the water has undergone, especially the GAC filtration.) Finally, the water is aerated: air flows through it to adjust its pH level, so that it’s non-corrosive–in the case of Buffalo Pound water, a fairly minor adjustment.
Then, of course, the water is pumped to your home, a service for which you cheerfully pay the city a small fee on a regular basis.
At least, you ought to pay cheerfully: after all, if the city didn’t provide this service, we’d all be hauling water out of Wascana Creek with buckets.
Think of that next time you’re paying your water bill, and smile.
