Posts Tagged ‘potable water’

Lately, when I wash dishes, take my shower, or turn on the washing machine, I’m thinking about my walk though the vast, dark, cavernous filtration gallery at Montreal’s Charles-J. Des Baillets water filtration plant. I’m thinking about the sixty basins of water filtering through their four-foot-deep beds of sand. I’m thinking about the deafening noise of the plant’s pumps. I’m thinking about the molecules darting around in the gigantic ozonizers that kill bacteria and viruses. I’m thinking about the 20 Megawatts per day it takes to do all this.

And that’s just one of seven plants serving the Montreal territory.

Each day, pumps draw water from the St. Lawrence River, Lac Saint-Louis, Rivière des Prairies and Lac des Deux Montagnes to supply the island with drinking water. The water is filtered, disinfected and chlorinated, sent to water reservoirs for storage, and then carried though a distribution network of pipes to businesses and homes.

Filtration Gallery tech sheet: "60 filtering beds divided into four units of 15 double filters, each having 4.9 m by 16.5 m tanks"

After we’ve used the water and flushed our toilets, it goes through another network of pipes to the island of Montreal’s wastewater treatment station, where it is cleaned as much as possible before being dumped back into the St. Lawrence River. (But we’ll talk about that another day.)

Like last fall’s excursion to the city dump (um, sanitary landfill), my visit to the Charles-J. Des Baillets filtration plant in LaSalle was organized by the Société environnementale Côte-des-Neiges (SOCENV). These visits are part of a program for integrating immigrants into Quebec society, but anyone is welcome to participate.

Noisy pumps. For the tour, our guide spoke into a headset and we wore earphones.

The Des Baillets plant is the island of Montreal’s second biggest, producing 1.136 million cubic metres of drinking water per day. The biggest is the Atwater plant, producing 1.364 million m3.  Both plants draw their water from the depths of the St. Lawrence River, just upstream from the Lachine Rapids. Together, they produce 88% of the island’s potable water.

The water treatment process

In operation since 1978, the Des Baillets plant is a bit different from the Atwater plant because it uses ozonation to disinfect the water. “Ozonation . . . produces water of superior quality than that obtained from the classic chlorination process,” the plant’s literature states. Some chlorine is added at the end of the process, but this is just to make sure the water remains sterile until it reaches your tap (or the tap of your friend who lives on the far end of the distribution system).

Here’s how it works:

1. Water goes through a rough screening at the point of intake to prevent the passage of larger substances or objects. It is then pumped up to the top of the filtration plant, so that gravity can carry the water through the rest of the plant’s processes.

2. In the filtration gallery, the water goes through double filters that use 1.2 m of siliceous sand, eliminating about 80% of organic substances, bacteria and viruses.

The insides of an ozonizer (one not currently in use, that is!)

3. Next, ozone is injected. This destroys any remaining bacteria and viruses. The ozone is then destroyed in powerful ovens. Note: at the moment, the ozone is extracted from the air; however, the plant is undergoing renovations to use pure oxygen instead.

4. At this point, the water is suitable for human consumption. However, to keep the water sterile throughout its distribution, a small dose of chlorine is injected before it is pumped out to the reservoirs. (In the plants that do not use ozonation, chlorination is part of the disinfection process.)

Montreal has seven drinking water production plants. The five on the west of the island have reservoirs, at the plants or along the network, with a total capacity equivalent to 32 Olympic pools. The Des Baillets and Atwater plants have on-site reservoirs with capacities equivalent to 121 and 66 Olympic pools respectively. But they supply six reservoirs located on and around the summit of Mount Royal, with a total capacity of over 600,000 m3 (160 Olympic pools). Gravity is then used to send the water through the city’s distribution system.

Mmm, mmm, good

The water is tested when it comes out of the plant, of course, but also all along the network, every day. Standards and parameters (including those relating to chlorine) are set out in Quebec’s Regulation respecting the quality of drinking water. During the visit, our guide noted that the plant will soon be adding UV treatment, to further improve the water quality.

I’m not going to get into the tap water vs. bottled water debate here. But I think it’s safe to say that (1) Montreal has excellent tap water; and (2) the environmental impact and energy costs of bottled water far exceed those of potable tap water.

On the issue of whether tap water or bottled water is better for your health, the Quebec organization Eau Secours did a study a few years ago, comparing applicable laws, regulations and quality controls for the two types of water. You can read their conclusions online : “Eau du robinet versus eau embouteillée: laquelle est la plus sécuritaire?” They also have a campaign about the safe reuse of plastic bottles: see their brochure, “La réutilisation des contenants de plastique d’eau embouteillée et la santé.” (Both links in French only, sorry.)

And now, I’m off to have a cup of tea — made from freshly boiled and brewed Montreal tap water.


City of Montreal: “Production de l’eau potable” and in particular, “Le saviez-vous?” (a sort of FAQ page)

Eau Secours, a Quebec coalition that advocates responsible water management

Info about the UN “Water for Life” Decade

Aquanomy, a site devoted to water conservation in the home

And an interesting article that appeared recently in The Economist, reminding us that not everyone has free and easy access (or any access) to safe drinking water: “The worth of water.”


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