Drinking water… from the river to your tap

Water supply presupposes that the water will be treated to make it drinkable and treated once again before returning it to nature.

The St. Lawrence River is the source of Longueuil's drinking water. To supply industry, businesses and homes, Ville de Longueuil operates three water treatment plants. Once treated, water is stored in one of five immense reservoirs to be distributed through an impressive network of pumps and water mains. Once finished with, the used water is collected through a network of sewers and is treated before being returned to the river from which it was drawn.

Comply with regulations on the use of drinking water

Ville de Longueuil adopted in September 2008 a by-law concerning the use of drinking water. The provisions of the by-law include, among others, watering lawns, washing vehicles, filling pools and restrictions of use. For more information, see the section of Main by-laws.

Water that is minutely analysed … and is economical!

As well as carrying out regular analysis at the filtration plant with sophisticated equipment, a team of technicians carries out a battery of tests daily:

  • 105 bacteriological analyses
  • 235 physical and chemical control analyses
  • 301 analyses for residual chlorin

An independent control laboratory also checks the bacteriological quality of the water at various points in the distribution networks, which represents yearly around:

  • 520 samples on Boucherville's network
  • 310 samples on Saint-Bruno-de-Montarville's network
  • 2185 samples on Longueuil's networks
  • 990 samples on Brossard's network
  • 310 samples on Saint-Lambert's network

As an example, a family of four people uses an average of 10,000 to 12,000 litres of water a week. Nevertheless, even if the production cost of drinking water is low, it shouldn't be wasted because this resource is not inexhaustible.

Drinking water treatment and distribution by the numbers

Drinking water production statistics

Population served: 419,677 people

Total production capacity of the three treatment plants: 448,000 cubic metres per day
Average daily production: 221,200 cubic metres per day, or 49% of production capacity, the equivalent of 88 Olympic-sized pools
Daily average per person: 527 litres per day/per person

Water mains and sewer network

Water mains network: 1,630 km of pipes
Sewer network: 2,478 km of pipes
Other installations: 38,189 manholes and 9,441 fire hydrants

Reports on drinking water quality

Three water filtration plants serve the whole of the agglomeration

Two plants are located in the borough of Vieux-Longueuil and one in the city of Saint-Lambert. The largest of the three serves residents in Vieux-Longueuil, Boucherville, Saint-Hubert and Saint-Bruno-de-Montarville, almost 260,569 people. It is the second largest water filtration plant in Quebec, the largest being in Montreal. A second, smaller installation serves those people living in the immediate area around the plant in Vieux-Longueuil, almost 27,534 people. Finally, a third filtration plant, located in Saint-Lambert, serves residents in the Saint-Lambert, Greenfield Park, Le Moyne and Brossard areas, around 131,574 people.

Regional treatment plant

Regional Treatment PlantThe main treatment plant in the borough of Vieux-Longueuil has undergone various extensions since it began operating in 1956. It currently covers an area of some 10,000 square metres. In 1982, it was completely modernized to increase its production capacity to almost 265,000 cubic metres of water per day. In 2015, a new ultraviolet disinfection step is added to the drinking water treatment process. A central command post is located at the plant where a team of operators controls both the plant itself, the raw water supply station, the Julien-Lord reservoir (Vieux-Longueuil), the Kimber reservoir (Saint-Hubert), the Montbrun reservoir (Boucherville) and the Normandie reservoir (Boucherville) on a round-the-clock basis.

To ensure a high level of quality for consumers, sophisticated equipment is used in the treatment process. Four dynamic decanters of the “pulsator” type, and twenty-six high charge filter units with sand and anthracite beds ensure the final treatment. Two chemical products - aluminium sulphate and a polymer are used for coagulation, while a third — gaseous chlorine — ensures that the water is thoroughly disinfected.

The drinking water is then passed to reservoirs having a 55,000 cubic metre capacity located underneath and around the plant. This water is constantly changed to ensure it remains fresh.

Distribution of drinking water is assured by a group of four electric pumps capable of propelling 273,000 cubic metres of water a day into the network. To ensure an uninterrupted supply of water to this large clientele, three diesel pumps can take over during a power failure and provide a supply of 204,000 cubic meters of water a day.

The main plant in the borough of Vieux-Longueuil also supplies various reservoirs on the network. These networked reservoirs, along with the plant's reservoir, constitutes a volume of drinking water of nearly 150,000 cubic metres.

For information, please contact: Direction de la gestion des eaux

Local treatment plant

A smaller plant serves the immediate area in the borough of Vieux-Longueuil, around 27,534 people. It was built in the 1940s to meet the ever-growing demand for water and has undergone several renovations. These renovations increased the plant's capacity to almost 40,000 cubic metres of water per day. The last change was made in 2014 when a new ultraviolet disinfection step was added. Once treated, this water is stored in reservoirs having a capacity of 9,000 cubic metres and located under and at the side of the treatment plant.

Le Royer Filtration PlantThe Le Royer filtration plant

Located in Saint-Lambert, the Le Royer installation serves the populations of Saint-Lambert, Greenfield Park, Le Moyne and Brossard, some 131,574 people. It has a treatment capacity of 137,500 cubic metres per day, but its average daily production, to meet current requirements, is 53,600 cubic metres per day.

Drinking water production in five steps

1. Raw water screening and pumping

Raw water screening and pumping

The pumping station collects raw water from the St. Lawrence River. The water then passes through a degritter and is carried to the treatment plant through pressurized pipes.

In the fall, activated charcoal dust is added to the raw water to improve its taste.

2. Flocculation


When the raw water arrives at the regional plant, it passes through tanks at high speed. These tanks are located in the mixing room where other chemicals are added to the raw water.

Under the action of aluminium sulphate and a polymer, a floc is formed as a result of the combination of chemicals and suspended solids in the water. Under a microscope, this floc resembles snowflakes.

3. Settling


From the mixing room where it remains only a very short period, the water is pumped into dynamic settling tanks where it is clarified and from which flocculated suspended solids are extracted (removal of concentrated sludge).

The process consists in introducing the raw water with its reagent into a vacuum chamber. When the water reaches a certain level (phase 1), a control device opens a valve and vents the vacuum chamber (phase 2).

At the surface of the tanks, a system of troughs continuously collects the clarified water. This water is however not yet fit for consumption, and still has to be disinfected and filtered.

4. Filtration


Just before filtration, the water undergoes a first disinfection stage with the addition of chlorine gas (interchlorination).

At this stage, the water passes through a bed of sand and anthracite. This operation removes all remaining particles from the water.

The filters are cleaned on a regular basis to ensure the water's highest quality at all times.

5. Postchlorination (Cl₂)

Postchlorination (Cl₂)

The drinking water then flows into reservoirs having a total capacity of 55,000 cubic metres. The reservoirs are located under and alongside the plant.

The water is constantly renewed to maintain its freshness.

Waste water treatment

To be respectful of the environment, the cycle of water would be incomplete without waste water treatment. Thanks to the South Shore Waste Treatment Centre, water that is taken from the St. Lawrence River is returned to it in a cleaner state than when it was drawn off. To learn more, read the section Waste Water Treatment.