A friend invited me to participate in a charity walk of 5 km on 29 August 2014, through a picturesque trail in the city to raise awareness about the problem of safe drinking water faced by millions worldwide and also to raise money. The Walk for Water was in support of Water Missions International’s response to the global water crisis through sustainable safe water and sanitation solutions around the world. Safe water is the source of life. It is the foundation for health, education and viable economies. The global safe water crisis is much more than just a lack of safe water. Providing those people with access to safe water gives them an opportunity – an opportunity to go to school, work and play free from the stress of dirty, disease-filled water.
There were posters put up all along the path depicting the problems faced by people all over the world. There were posters saying how lucky the Canadians are as they have the Great Lakes and thousands of smaller lakes with clean potable water. Canadians are blessed with clean municipal water supply all through the day year around.
This prompted me to study the municipal water supply system in our City of Mississauga, which comes under the Peel Region.
Lake Ontario is the source for the Peel Drinking Water System. As the lake water enters the intake, located about 2 km from the lake-shore, it is chlorinated. The chlorine kills bacteria and prevents mussels from growing in the intake pipe and obstructing the flow. As the water enters the treatment facility, it passes through travelling screens. The screens prevent items such as fish, sticks and aquatic plants from entering the treatment facility and damaging equipment. Water is then treated by means any one of the following treatments based on the age of the plant.
- Conventional treatment.-
- Alum, a coagulant is added to the water. The rapid mixer thoroughly mixes the coagulant with the water to help form sticky particles from the suspended particles in the water.
- Slow mixing that helps the sticky particles collide with each other, forming larger and heavier particles called floc.
- Floc particles are removed from the water by inclined plate settlers or the water is slowed down in large tanks to allow particles to settle to the bottom.
- Removes remaining particles and chlorine-resistant bacteria and reduces the levels of compounds that can cause tastes and odours. The water travels down by gravity through layers of granular activated carbon, sand and gravel.
- Ozone Biologically Activated Carbon Contactor and Membrane Filtration (OBM) Treatment.
- Ozone gas is bubbled through the water in the Ozone Contactors. Ozone kills bacteria and also helps to break down substances that cause tastes and odours so that they can be removed easily.
- BACC Filters: These specially designed contactors remove the biodegradable organic matter produced by the activity of the ozone process. This removal process keeps the water stable after treatment by minimizing re-growth of bacteria in the distribution system.
- Membrane Filters: These are specially designed water filters with very small pores that the water is pulled through. The membrane filters remove microorganisms and producing water with very little turbidity.
- The modern state-of-the-art Membrane Filtration, Ultraviolet Light, and Granular Activated Carbon Contactor (MUG) treatment.
- Membrane Filtration. Raw water is pulled through state-of-the-art Ultra Filtration Membranes with pores small enough to filter out particles and many microorganisms.
- UV Light. Filtered water then passes through UV Light Units, which inactivate microorganisms. These units also reduce taste and odour in the water by Advanced Oxidation. The Advanced Oxidation process uses hydrogen peroxide and a higher intensity of UV light to oxidize (break apart) compounds that cause unpleasant taste and odour. The Advanced Oxidation system is used seasonally, when taste and odour problems are at their peak due to lake and temperature conditions.
- Granular Activated Carbon Contactor (GACC). The water then flows down through a matrix of carbon granules into GACC. They eliminate any residual hydrogen peroxide from the Advanced Oxidation process.
Water treated by any of the three above processes is further treated prior to supply into the water supply system as under:
- Chlorination for inactivation of bacteria/ disease causing organisms.
- For better dental health and to protect teeth from cavities
The water is then supplied through the pipes, buried 10 feet below to prevent freezing in winter. The old ductile iron pipes (DIP) forming the water mains, running mostly below the municipal roads, are now being replaced with polyethylene encased DIP, which has a lifespan of up to 100 years.
Majority of the water main replacement projects are undertaken from March to October every year, in partnership with road and sewer renewal projects for improved cost effectiveness and minimized public inconvenience. This prompted a friend to remark that in Canada we have four seasons – winter, severe winter, winter and then construction.
How do they ensure water at the optimum pressure throughout?
A typical municipal water supply runs at between 50 and 100 psi (major appliances require at least 20 to 30 psi). Pumps at the water treatment plant pumps water at about 100 psi and is connected to the main pipe lines. There are three water towers in the city which are also connected to the same pipeline. During low water usage hours, the tanks on the water towers get filled and they discharge into the pipeline when the pressure falls due to high usage during peak hours, thus maintaining the optimum pressure. There are no overhead tanks in the homes as the city guarantees 24 hours water supply at optimum pressure.
As the water in the pipelines is maintained under high pressure all throughout, there is hardly any chance of muddy water from the ground getting into the pipes. Mixing of dirty water or sewage is possible only when there is intermittent water supply and there is a crack in the pipe. The water in the pipe leaks into the soil around when under pressure. When the water supply is shut down, the pressure in the water pipes drop below the pressure of water in the soil, forcing the muddy water into the pipeline through the crack. When the water supply is restored, this muddy water in the pipes reaches the consumer.
How come the water in the water towers do not freeze in the cold Canadian winters?
They do freeze. They just don’t normally freeze solid. The central pipe that runs from ground level up into the bottom of the tank is called a riser. Many tank risers are wrapped with heat tape, covered with insulation and capped by an aluminum jacket. Ice forms on the surface of the tank, in many cases several feet thick. Normally, this ice layer floats on the surface as the water level rises and falls. Many times this ice remains stuck to the roof the tank and remains there.
This is why the City of Mississauga proclaims that the best drinking water is the municipal water.