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What's in the water?

The sources of drinking water in Durham Region include both surface (lake) water supplies and groundwater supplies.

The filtration process used to treat the water at a Surface Water Plant includes  chemical treatment.  The chemical used has properties that cause the finer particles in the raw water to clump together into larger ones, making them easier to be filtered out.  Following the chemical treatment, the water is filtered to remove the suspended particles.  Chlorine is added at various stages of the process to kill, or inactivate, any disease-causing organisms.   A free chlorine residual is maintained in the distribution system to protect the water from microbiological re-contamination, re-growth and to control biofilm formation.

Regional groundwater supplies are derived from wells, which tap into aquifers.  (An aquifer is a deposit of saturated granular soils).  Groundwater is naturally filtered and so typically contains few or no disease-causing organisms.  Treatment of groundwater consists of disinfection with chlorine and at some locations disinfection is supplemented with Ultra-Violet disinfection.   Additional treatment of some of our groundwater supplies for chemical control of dissolved minerals such as iron is performed by adding sodium silicate to keep iron in suspension (moderately elevated iron levels can cause reddish discolouration and deposition when exposed to air).   A free chlorine residual is maintained in the distribution system to protect the water from microbiological re-contamination, re-growth and to control biofilm formation.

The following outlines various groups of parameters, which may be present in the source water

Bacteriological Parameters:
Bacteriological quality is the most important aspect of drinking water quality because of its association with dangerous water-borne disease, which can strike quickly.

Inorganic Parameters:
Inorganic parameters such as salts and metals can be naturally occurring or a result of urban storm runoff, industrial or domestic wastewater discharge, mining or agriculture.  Some may be a result of treatment and distribution of drinking water.

Organic Parameters:
Organic parameters can be naturally occurring, but most organics of concern are synthetic.  They originate from industrial discharges, urban and agricultural runoff, and other sources.  Included in this group are pesticides, herbicides, solvents, that originate from both rural, urban, and industrial areas.  Some synthetic organics may originate from the treatment of drinking water (for example chlorination by-products such as trihalomethanes).  Most synthetic organic chemicals are present at low concentrations.

The presence of these substances in drinking water does not pose a health risk when the Ontario Drinking Water Quality Standards are met.