Page 2: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Turbidity

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Part I: Overview and Application

1.0 Guideline

Turbidity levels are an important consideration for the effective design and operation of a variety of treatment processes and as an indicator of water quality changes in drinking water systems.  For filtration systems that use conventional, direct, slow sand, diatomaceous earth or membrane technologies, the turbidity from individual filters or units should meet the following treatment limits in order to achieve health-based pathogen removal goals:

1. For conventional and direct filtration, less than or equal to 0.3 nephelometric turbidity units (NTU) in at least 95% of measurements either per filter cycle or per month andnever to exceed 1.0 NTU ;
2. For slow sand or diatomaceous earth filtration, less than or equal to 1.0 NTU in at least 95% of measurements either per filter cycle or per month and never to exceed 3.0 NTU ; and
3. For membrane filtration, less than or equal to 0.1 NTU in at least 99% of measurements per operational filter period or per month. Measurements greater than 0.1 NTU for a period of greater than 15 minutes from an individual membrane unit should immediately trigger an investigation of the membrane unit integrity.

Other considerations:

The aforementioned filtration systems should be designed and operated to reduce turbidity levels as low as reasonably achievable and strive to achieve a treated water turbidity target from individual filters of less than 0.1 NTU.

To ensure effectiveness of disinfection and for good operation of the distribution system, it is recommended that water entering the distribution system have turbidity levels of 1.0 NTU or less. For systems that are not required to filter by the appropriate authority, a higher turbidity level may be considered acceptable, provided that it does not hinder disinfection.

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