Treatment for Chemical and Physical Parameters

In addition to standards for the microbiological quality of drinking water, the Guidelines for Canadian Drinking Water Quality (GCDWQ) have health-based water quality criteria for chemical and physical parameters (parameter refers to the minerals, chemicals, bacteria, etc. that are tested in a water sample by using an accredited water testing laboratory). Physical parameters include:  colour, odour, taste and temperature. Water quality criteria for radiological parameters are also provided in the GCDWQ.

• Maximum Acceptable Concentration (MAC) is a level that has been established for certain substances that are known or suspected to cause adverse health effects. For water to be considered potable, a water treatment system must be capable of providing water that does not exceed the MAC for any parameter listed in the GCDWQ (as shown in the Summary Tables). 

• Aesthetic Objectives (AO) are established for parameters that may impair the taste, smell, or colour of water; or which may interfere with the supply of good quality water. Aesthetic effects play a role in determining whether consumers will consider water drinkable. They do not cause adverse health effects. Water suppliers are encouraged to treat water to ensure that an AO for a particular chemical does not unreasonably exceed the level set in the guidelines.

• Operational Guidance Values (OG) relate to water treatment processes that treated water must meet before it enters the distribution system. This is also referred to as an ‘operational water treatment guideline’, Operational considerations are factored in when the presence of a substance may interfere with or impair a treatment process or technology (e.g., turbidity interfering with chlorination or UV disinfection) or adversely affect drinking water infrastructure (e.g., corrosion of pipes).

Pathogen Log Reduction for Different Source Waters

For surface water and groundwater at risk of containing pathogens (GARP) sources, two methods of treatment (dual treatment) are required. Most treatment systems require clear water to ensure maximum efficiency. Following the multi-barrier approach, the Canadian Drinking Water Guidelines recommend that filtration and one form of disinfection be used to meet the treatment objectives and provide the most effective protection against waterborne pathogens (bacteria, viruses and protozoa). For more information, see the Drinking Water Treatment Objectives (Microbiological) for Surface Water Supplies in British Columbia and the Drinking Water Treatment Objectives (Microbiological) for Ground Water Supplies in British Columbia).

What is Log Reduction?

Log reduction and/or inactivation is a mathematical term used to express the relative number or percent of viable microorganisms reduced/inactivated (killed or unable to replicate) by a disinfectant. The reduction/inactivation of microorganisms is generally measured on a logarithmic scale which is based on factors of 10 (i.e. 10 fold increases or decreases). 

You’ll find a more thorough explanation on our Minimum Treatment Objectives and Pathogen Log Reduction page.

Minimum Pathogen Log Reduction for Different Source Water Types

The BC drinking water treatment objectives recommend minimum pathogen log reduction for protozoa and viruses based on source water type (shown below in Table 1). For water systems in BC using surface water or GARP sources, treatment barriers must be in place that are capable of providing at least 3-log (99.9%) reduction of Cryptosporidium and Giardia, and 4-log (99.99%) reduction of viruses that may be present in the source water.