Water stays in the pipes longer in shrinking cities – a challenge for public health

The geographic locations where Americans live are shifting in ways that can negatively affect the quality of their drinking water.

Cities that experience long-term, persistent population decline are called shrinking cities. Although shrinking cities exist across the U.S., they are concentrated in the American Rust Belt and Northeast. Urban shrinkage can be bad for drinking water in two ways: through aging infrastructure and reduced water demand.

Major federal and state investments in U.S. drinking water occurred after the World Wars and through the Drinking Water State Revolving Fund created by the 1996 amendments to the Safe Drinking Water Act. Many of the pipes and treatment plants built with those funds are now approaching or have exceeded the end of their expected lifespan. Shrinking cities often don’t have the tax base to pay for maintenance and replacement needs. So the infrastructure, which is largely underground, out of sight and out of mind, deteriorates largely outside of the public eye.

Water systems are typically designed for growth, not shrinkage. Oversized water treatment and distribution systems are common in shrinking cities that experience less water demand than they did decades ago. Consequently, shrinking cities can have drinking water sit in their old and corroded distribution system pipes longer than desired. The water age, or time water spends in pipes from treatment to consumption, increases. As engineers, scientists and public health professionals, we are studying the health effects of drinking water and concerned that not enough attention is being paid to what high water age can mean for public health.

More time in the pipes

In the early 2000s, the U.S. Environmental Protection Agency published a report about how high water age causes undesirable changes in the chemical, microbiological and physical quality of drinking water. Examples of water quality factors that can deteriorate with increased water age include levels of disinfection byproducts, corrosion, microbial growth (including pathogens) and nitrate. Each of these factors can directly affect public health.

As an example, there’s been a major shift in the type of microbes that cause waterborne disease outbreaks in the U.S. since the EPA report was published. In 2002-2003, two-thirds of these outbreaks involved bacteria that cause diarrhea, and approximately a quarter of outbreaks were due to pneumonia that can occur when vulnerable people breathe in contaminated water while showering, for instance. In the most recent report, covering 2011-2012, the statistics reversed, with pneumonia (mostly due to Legionnaires’ Disease) accounting for two-thirds of all outbreaks and 100% of all waterborne deaths during the monitoring period.

High water age contributes to low chlorine concentrations and corrosion, which can result in high levels of metals, such as iron. When these conditions occur during warmer summer months, growth of Legionnaires’ Disease bacteria increases. Low levels of disinfectant can also increase total bacteria in drinking water and support growth of some bacteria that can be unhealthy for the youngest, oldest and most ill consumers.

Importantly, routine monitoring of microbiological indicators in U.S. drinking waters hasn’t changed much since the Safe Drinking Water Act was passed in 1974. It still centers on detecting organisms that can cause diarrhea, not respiratory illnesses like pneumonia, and it is assumed that treatment methods that address the former will remove the latter.