Guidance For Safe Drinking Water In Canada: From Intake To Tap

Assessment of the Drinking Water Supply

A comprehensive multi-barrier drinking water program includes:

• Source water protection
• Sanitary surveys of the source area and distribution system to identify and prioritize risks to health
• Watershed or well-head protection plans
• Expansion capacity for forecasted population growth
• For treated water, continuous optimal treatment
• Routine maintenance of the distribution system
• Treatment plant and distribution system classification, operator training and certification

The assessment of the drinking water supply forms the basis of all activities related to providing the cleanest, safest, most reliable drinking water to the public. Assessments identify the characteristics of the water source, potential hazards, how these hazards create risks and how these risks can best be managed. The drinking water supply includes everything from the collection of the raw water to the point where the water reaches the consumer.

Selecting source waters

The first step in implementing a drinking water program is to identify water to be used as the source of drinking water. At this stage, an assessment should be made of the potential risks associated with the source. Risks could include wildlife in a watershed, recreational activities such as boating in a reservoir, wastewater treatment plants nearby, agricultural or industrial activities, etc. The system should be designed to minimize the impact of the risks over time. The characteristics of the source water - including physical (such as aquifer characteristics for groundwater sources), microbiological and chemical parameters, and the types of natural and anthropogenic contaminants present - determine the type of treatment required in order to deliver the cleanest, safest, most reliable drinking water to the public. Wherever possible, the system chosen should also be capable of being adapted to deal with unforeseen contaminants.

Groundwater wells, intakes and raw water reservoirs

Some of the key characteristics in the design and the construction of groundwater wells, intakes and raw water reservoirs are the location, size and capacity, seasonal variations, retention times, design period, etc. In assessing these components, all potential hazards and their causes should be identified, and the level of risk associated with each of the hazards estimated, so priorities for risk management action can be established.

Treatment system

Treatment systems should be designed based on the site-specific raw water quality. Seasonal variations should be taken into account. Characteristics include treatment processes, treatment components, equipment design, chemicals used, treatment efficiency, monitoring procedures, etc. The treatment selected should address all potential hazards and the level of risk associated with those hazards.

Treated water reservoir, service connections and distribution system

Treated water reservoirs and distribution systems should be designed to take the following into account: access by wildlife and people, system capacity, emergency water storage, contact time required for disinfection, minimizing or eliminating dead ends, and cross-connection controls. They should also be designed and constructed in compliance with all local or provincial by-laws, best management practices and regulations.

Drinking water purveyors and consumers should be advised when purchasing materials that will come into contact with their drinking water (such as chemicals, plumbing materials or water filters) to buy only certified products which meet recognized health-based performance standards. This caution is particularly important for consumers purchasing off-the-shelf products which they will install themselves; licensed home builders and plumbers are required to install only certified products into homes in order to meet the requirements of plumbing codes. Nonetheless, proper operation and maintenance of these products by the consumer are equally important to reducing the risk of illness.