Filtration and Disinfection Monitoring Requirements
Public water systems that use surface water—or groundwater that is directly influenced by surface water—must remove or sufficiently inactivate microbiological contaminants to ensure that drinking water is safe. This requires at least two pathogen barriers, one to filter and one to disinfect. Water systems confirm proper filtration and disinfection by monitoring for turbidity, chlorine, pH, and temperature. We may cite systems during sanitary surveys if they are not properly monitoring for each parameter. For filtration, the state’s drinking water regulations establish performance criteria based on surrogate monitoring of turbidity, which is the industry standard. For chemical disinfection, performance criteria are based on pH, temperature, and chlorine residual, which correspond to an estimated treatment using log inactivation equations. Appropriate monitoring consists of several key steps.
Key steps
- Monitoring in the correct locations
- Selecting appropriate equipment/instruments to monitor the parameter in question
- Using proper techniques to monitor
- Calibrating and verifying instruments in accordance with state and federal requirements
Turbidity
- Online turbidity analyzers must be calibrated quarterly
- Continuous monitoring means that measurements must be recorded at least every 15 minutes
- Signals should be averaged over about 30 seconds to 1 minute but must not be averaged over 3 minutes
- Results should be verified once per week with an alternative method, but this is not required
Chlorine analyzers
- Online chlorine analyzers must be verified with a handheld method once per week
- Continuous monitoring means that measurements must be recorded at least every 15 minutes
- Signals should be averaged over about 30 seconds to 1 minute but must not be averaged over 3 minutes
pH/Temperature
- Must be analyzed immediately after collection and never sent to the lab
- pH must be calibrated daily
A few systems in Colorado disinfect with ultraviolet light, chlorine dioxide, or chloramines, which require additional monitoring that will not be covered in this article. We work with systems that use these technologies on a case-by-case basis. Additional information can be found in our Policy 4 Guidance on Proper Operations of Water Treatment Processes.
Below are some resources that will give more specific information about the requirements outlined above. If you are concerned about your instrument monitoring system and calibration protocols, please contact Tyson Ingels at tyson.ingels@state.co.us.
Additional Resources
Colorado Primary Drinking Water Regulations
Safe Drinking Water Act
- Section 141.74 - Analytical and Monitoring Requirements
- Section 141.560 - Individual Filter Turbidity Requirements
➽ Tyson Ingels, lead drinking water engineer
