Disinfection & Distribution

Distribution System

About disinfection

Drinking water is disinfected to kill pathogenic bacteria, viruses and protozoa.

Drinking water disinfection, which began in the United States in 1908, has been heralded by the Centers for Disease Control and Prevention as one of the 10 greatest public health improvements of the Twentieth Century. Disinfection is one component of the multi-barrier approach to water treatment that also includes source water protection, sedimentation, filtration and maintaining the integrity of the distribution system.

From a regulatory perspective, disinfection is required by the Safe Drinking Water Act. Regulations also require disinfection of reused water and wastewater discharged to streams and lakes. Regulations also address the harmful effects of certain disinfection byproducts, the corrosion of lead and copper into water supplies and the safe and secure use of disinfectant chemicals such as chlorine gas.

Read more about disinfection regulations.


About distribution systems

Disinfection at a water treatment plant is the first step in ensuring the safety of water that reaches household taps. Once disinfected water leaves a plant, it must travel through a complex distribution system of pipelines and storage facilities that can stretch for many miles. In the United States, the distribution systems of public drinking water supplies span almost 2 million miles and include an estimated 154,000 treated-water storage facilities.

Given the extensive nature of distribution systems, much of which is buried, ensuring the safety of distributed water is a significant challenge for water systems, regardless of the size of community served. And as this water infrastructure ages, the job is made that much more important, and expensive.

The regulations that have been put in place to protect the safety of distributed water fall into two categories: 

  • The Surface Water Treatment Rule and the Total Coliform Rule to ensure the microbial quality of the distributed water, and
  • The Disinfection By-Products Rule and the Lead and Copper Rule to ensure that the distributed water prevents the continued increase of disinfection by-products and to prevent corrosion from infrastructure components that contain lead and copper. 

To that end, water utilities routinely monitor chlorine residual, coliform occurrence, disinfection byproducts, lead, copper and pH from treatment plant to tap.