Selecting Disinfectants

Supporting Resources • Regulations • Risk Communication • Disinfection Practices • Safety & Security

Chemical disinfection of public drinking water supplies, started in the United States in 1908 with the use of chlorine, has been heralded by the US Centers for Disease Control and Prevention as one of the 10 great public health improvements of the twentieth century to control infectious diseases. This global water treatment practice is one component of the multibarrier approach to water treatment that also includes source water protection, sedimentation, filtration, and maintaining the integrity of the distribution system.

Disinfection of public water supplies as well as reused water and wastewater discharged to streams and lakes is required in the United States by federal regulations implementing provisions of the Safe Drinking Water Act and Clean Water Act, and some states have imposed additional requirements for disinfection. Since disinfection became a public health practice in the early twentieth century, both our understanding of disinfection and available disinfection technologies has significantly improved. Disinfectant selection is central to the design and operation of drinking water, wastewater, and reuse systems.

Fully considering the pros and cons of the suite of treatment options available to the water sector is increasingly an aspect of utility decision-making, and this is especially true of disinfectant selection.  As our understanding of drinking water treatment and water quality improves and the water sector tackles community and personnel safety concerns, appropriate levels of disinfection must be maintained while responding to many more decision criteria. As disinfectant selection becomes more complex, the importance of undertaking a transparent, well-informed, goal-driven selection process becomes more and more critical.

Selecting Disinfectants in a Security Conscious Environment

One resource that can inform that process is AWWA's guide for drinking water and wastewater systems, Selecting Disinfectants in a Security Conscious Environment.  This guide, published in 2009, describes a step-by-step process to evaluate disinfection options that meets the unique needs of each water, wastewater, and reuse system. Available in the AWWA Bookstore, the product builds on existing water sector engineering practices, manuals of practice, costing tools, and public communication techniques to

• address federal and local statutory and regulatory disinfection objectives;
• reflect local circumstances;
• compare disinfection options consistently;
• consider operational, process, and supply-chain reliability as well as environmental, operator, and community safety considerations;
• provide transparency in the decision-making process; and
• incorporate appropriate risk communication within the decision-making process and the community.

Note: AWWA Utility Members have been informed how to download this report for free.

5-Step Process

The guide details a 5-step process for selecting disinfecants:  

1. Assess Current Situation
Identify existing and future disinfection requirements and regulations and the ability of the existing disinfection process to meet them. Review past water quality and security assessments and recommendations and determine which recommendations have been or are planned to be implemented. Use the information gathered to establish system disinfection goals and objectives.

2. Identify Options
Use a screening process to determine which disinfection options are feasible to carry forward for detailed evaluation.

3. Evaluate Options
Evaluate each disinfection option identified as feasible in step 2 by defining and then comparing and contrasting the attributes, costs, advantages, and disadvantages of each option. This evaluation can reflect on design considerations such as reducing the quantity of hazardous substances stored on-site; the reliability and efficiency of potential disinfectant system options; and simplifying treatment processes where possible.

4. Select Option
Use the results of the evaluation along with decision-making tools to select the preferred disinfection method.

5. Implement Selected Option
Design, install, construct, and start up the facilities and equipment required to implement the preferred disinfection method.

Decision-Analysis Tools

Decision-analysis tools help inform a decision, not to make a decision. When used, these tools can lead to more confident decision-making. An important benefit of decision-analysis tools is that they can identify weaknesses in the input data and underlying assumptions that significantly affect the outcome of the analysis. Numerous decision-analysis tools are available.

Selecting Disinfectants in a Security Conscious Environment illustrates the use of two such tools: multi-attribute utility analysis (MAUA), and expanded social cost effectiveness analysis (ESCEA). CH2M Hill and Stratus Consulting prepared the following two spreadsheet tools that users can adapt to their own circumstances.

• MAUA Calculator (This entails "scoring" options that are being evaluated based on agreed-upon decision criteria, and doing so in an organized manner. This spreadsheet provides a simple tool for weighting ansd scoring criteria for a range of options.) 
• ESCEA Calculator