The Truth about Disinfection By-products in Drinking Water

Over the past few years, concerns have been expressed about US drinking water quality and source water protection. Many of these concerns are raised without context or perspective and may leave people with a distorted view of the overall role of disinfection and disinfection by-products (DBPs) in public health.

DBPs are unwanted substances in drinking water formed when disinfectants, such as chlorine, react with organic matter in the source water. This organic matter can be naturally decaying plant and animal matter or agricultural wastes. Some say DBPs in US drinking water create a risk to public health. The fact is that the drinking water community (which includes the Environmental Protection Agency (EPA), universities, utilities, and public health agencies) have worked together over the past 35 years to balance the benefit of disinfection (to destroy disease-causing germs) against the risks of DBPs, always remaining focused on public health through improved water quality. The result is water that is safe to drink.

The Great Balancing Act to Deliver Safe Water

The EPA directs municipal water utilities to disinfect raw water supplies to prevent waterborne disease outbreaks.  Before US cities began chlorinating drinking water (beginning in Jersey City, New Jersey in 1908), typhoid fever, cholera and dysentery were common killers, especially of children.  Drinking water chlorination represented a “public health revolution,” according to a new historical account of its adoption in the US, causing waterborne disease rates to plummet and life expectancy to soar.

Beginning in the 1970s, scientists began detecting low level concentrations of DBPs in treated drinking water. This discovery and investigations into the potential health effects of DBPs led to EPA regulation in 1979, followed by more stringent requirements in 1998.  As a result, the most common DBPs in drinking water are regulated to levels to prevent potential health effects. These levels are based on the best available science, incorporating a margin of safety.  In this way, EPA balances overall water quality by minimizing DBP levels without compromising disinfection.

A Smart Approach to Minimizing DBPs

To help control DBP formation, water treatment plant operators increasingly strive to optimize the removal of organic material, regardless of its source, before adding disinfectant to water.

It is certainly true that watershed protection measures can help reduce organic/agricultural waste entering source water. The basic tenants for protecting public health through public water supply are:

  • Select the best source available,
  • Treat it appropriately, and
  • Protect it in the delivery to the consumer.

Source water protection addresses the first of these, but steps are still required to reduce risks from naturally occurring contaminants as well as human-caused contaminants in source waters. Disinfection is necessary and required to guard against waterborne disease regardless of the quality of the source water and the extent of source water protection. Source water protection is good practice, but not a substitute for disinfection. We need both.

Maintaining a Holistic and Science-based Perspective

DBP research is a thriving field. When and if the weight of scientific evidence tips to support the need for lower regulatory limits on DBPs, EPA and the drinking water community should and will respond appropriately. Watchdog groups provide a valuable role in providing an outsider view in this important public health debate. Nevertheless, this discussion should remain grounded in science, with a holistic perspective on the benefits and any potential risks of drinking water disinfection.

Steve Hubbs retired from water treatment operations at the Louisville Water Company in 2004. He was involved in the development of the first DBP regulation in 1975-1979 and remains an active volunteer in the drinking water community today.