Page 4: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Ammonia
Part I. Overview and Application - Continued
Note: Specific guidance related to the implementation of drinking water guidelines should be obtained from the appropriate drinking water authority in the affected jurisdiction.
Free ammonia entering the distribution system can be one of the causative factors of nitrification and the potential increase of nitrate and nitrite in the distribution system. The health effects of nitrite and nitrate in drinking water and their respective MACs are fully discussed in the guideline technical document on nitrate and nitrite. Good operational practices will help prevent nitrification. These practices include limiting excess free ammonia entering the distribution system to concentrations below 0.1 mg/L (measured as ammonia-nitrogen), and preferably below 0.05 mg/L (measured as ammonia-nitrogen). Utilities using ammonia as part of their disinfection strategy should ensure that the appropriate chlorine to ammonia ratio is maintained. Changes in free ammonia concentrations can be an indication that nitrification is occurring; thus, monitoring should be conducted both at the treatment plant and in the distribution system.
Utilities should characterize their source water to assess the presence of ammonia and the variability of ammonia levels. Utilities that are chloraminating or that have ammonia in their source water should monitor for free ammonia, in addition to other parameters (e.g., total chlorine residual, nitrite, heterotrophic plate counts), at key locations in the distribution system. It is recommended that free ammonia be monitored daily in the plant effluent. In addition, it is recommended that source water, locations such as reservoir outlets and areas with long water detention times (e.g., dead ends) be monitored weekly. Changes in the trend of priority nitrification parameters in the distribution system, such as total chlorine residual, nitrite and nitrate, should trigger more frequent monitoring of free ammonia. Utilities that undertake comprehensive preventive measures and have baseline data indicating that nitrification does not occur in the system may conduct less frequent monitoring of free ammonia.