Deteriorating Water Distribution Systems Can Impact Public Health

Abstract

Distribution system infrastructure issues can affect water reliability and quality and could contribute to waterborne disease outbreaks. It’s important to know potential contamination mechanisms and consider rehab and replacement options.

Much of the US drinking water distribution system infrastructure was installed 50 or more years ago, which means a lot of it has exceeded its life expectancy and may be deteriorating. This can lead to increasing challenges for a historically reliable water supply and the barriers designed to prevent system contamination. Deteriorating drinking water distribution systems are prone to a host of problems that may increase the probability of public health issues. As distribution system infrastructure ages and replacement needs increase in the coming decades, infrastructure deterioration can be expected to be of more concern for drinking water utilities and may potentially have adverse effects on public health.

CONCEPTUAL FRAMEWORK

To analyze the public health effects of deteriorating infrastructure, we broke the problem down into smaller areas for analysis by developing a conceptual framework that includes the three broad areas shown in Figure 1 and detailed in the sections below: contamination mechanisms, infrastructure conditions, and waterborne disease estimates. These areas can be used to gauge how distribution system infrastructure deterioration may affect public health.

Figure 1. A Conceptual Framework.

Three areas can be used to gauge how distribution system infrastructure deterioration may affect public health.

Contamination Mechanisms.

It’s important to analyze how contaminants might be entering or increasing in the distribution system and which of these pathways may be influenced by infrastructure deterioration. For example, cross-connections may contaminate a water system, but the presence or absence of cross-connections isn’t necessarily affected by the distribution system’s condition.

Contaminants that affect public health may enter or accumulate within a water distribution system through several different mechanisms or contributing factors, some of which may be exacerbated by infrastructure deterioration. Although each mechanism is unique, the mechanisms may share causes and affect one another. Each mechanism may lead to contamination by itself or contribute to some combination of other mechanisms. Figure 2 shows a conceptual representation of the following contamination mechanisms affected by infrastructure deterioration and illustrates how each influences the others.

Figure 2. Contamination Mechanisms.

Contamination mechanisms may share causes and affect one another.

• Intrusion is the flow of nonpotable water into the water distribution system through leakage points or other openings. For intrusion to occur, distribution system pressure must drop below the external pressure of surrounding groundwater or sediment.

• Corrosion of metallic pipes and other fixtures can contribute to breaches that allow contaminants to enter the system. Iron corrosion can also lead to increased biofilm growth by providing increased surface areas for the colonization of biofilms as well as provide a protective niche from the effects of disinfectants.

• Biofilms are microbiologically produced organic polymer matrices containing microbes as well as organic and inorganic material. Biofilms themselves can increase the disinfectant demand and cause taste and odor issues as well as increase disinfection byproducts (DBPs). In addition, microbial activity in pipe biofilms is one factor that influences the rate of pipe deterioration.

• Sediment that accumulates in a pipe or storage facility can contain contaminants that enter through infrastructure breaches or pipes during pressure changes and subsequently enter the storage facility or piping. Sediments can also contain nutrients that can be a food source for pathogens living in the distribution system and can promote biofilm growth, which can protect pathogens from disinfectant residuals.

• Water age decreases disinfectant residual levels, which can leave the water more vulnerable to subsequent contamination. Increased water age is also associated with increased DBP levels, biofilm growth, and increased corrosion.

• Permeation is the passage of chemical constituents (e.g., gasoline-range organics) from outside of the distribution system through the distribution system material and into the finished water inside the pipes. Although this is typically considered as a potential concern in plastic, nonmetallic pipes, it can also occur through fittings, appurtenances, and some storage facilities.

• Leaching is the dissolution of material into the drinking water and can lead to the contamination of water by metals, organic contaminants, or asbestos. Unlike permeation, the leaching process is internal to the distribution system and doesn’t involve the introduction of outside contaminants.

Infrastructure Conditions.

It’s vital for a water utility to understand the state of its distribution system’s infrastructure which can affect these mechanisms. Drinking water distribution system infrastructure is composed of pipes (transmission lines and distribution mains), storage facilities (tanks and reservoirs), valves, pumps, and other appurtenances (e.g., pressure regulators and bulk meters). Each infrastructure component is vulnerable to different contamination mechanisms as it deteriorates. Customer service lines can experience some of the same problems as distribution system piping. In particular, lead and galvanized steel customer service lines can serve as a contamination source through corrosion.

Utilities can implement asset management programs to help make prudent, economically justified investments in distribution system infrastructure, as age alone isn’t a sufficient indicator of the need for infrastructure replacement. By following best practices in asset management, utilities can document the condition and failure history of their piping network and other assets to make better informed investment decisions. However, according to a 2015 USEPA Drinking Water Infrastructure Needs Survey and Assessment, many utilities are only in the early stages of developing an asset management program, as evidenced by the reliance of most survey respondents on the survey’s baseline pipe replacement rate. Developing a more comprehensive asset management program may help utilities better maintain infrastructure to reduce potential negative impacts on public health.

Waterborne Disease Estimates.

The presence of contaminants doesn’t always lead to people getting sick, and the presence of illness doesn’t always indicate water contamination. Therefore, it’s important to analyze any possible links between user illness and deteriorating infrastructure.

Although it’s difficult to quantify the public health impacts related to deteriorating distribution system infrastructure, several approaches can be used to provide estimates. These include using waterborne disease outbreak information to establish the potential extent of an adverse public health outcome and examining published reports or studies on waterborne disease (e.g., epidemiological studies) and modeled estimates of waterborne disease. Each of these approaches has its own strengths and weaknesses, but used together, they provide a better picture of the potential public health effects of deteriorating infrastructure.

Given the weaknesses in waterborne disease outbreak reporting and the time and expense needed to conduct epidemiological studies, it may be more valuable to use a modeling approach to estimate the amount of waterborne illness caused by deteriorating US distribution system infrastructure. A modeling approach could be supported by waterborne disease outbreak and epidemiological data. Further research is needed to determine appropriate proxies for infrastructure deterioration (e.g., pipe age, main failure rates, and water system budgets) and to gather data on a national scale associated with these proxies. Once an estimate of deterioration occurrence in the United States can be calculated, the relationship between deterioration occurrence and disease incidence could be further refined. However, deterioration isn’t a guarantee of drinking water contamination, and contamination itself isn’t a guarantee of illness. Further research is needed to be able to reasonably model these relationships on a national scale. On a local scale, increased awareness of the potential connections between infrastructure deterioration and public health can help water providers reduce the risk of drinking water associated waterborne illness.

REHABILITATION AND REPLACEMENT

Drinking water distribution system deterioration—when main breaks, pressure losses, biofilm accumulation, and other deficiencies become more likely—is a condition that can affect water supply and reliability as well as potentially endanger drinking water quality and public health. Several US waterborne disease outbreaks have occurred because of distribution system deficiencies, and more may occur in the coming years. It’s possible that deteriorating drinking water distribution system infrastructure has resulted in other cases of disease and illness, in addition to reported waterborne disease outbreaks.

Rehabilitation and replacement of deteriorating distribution system infrastructure will mitigate negative effects on public health. Drinking water utilities that are interested in funding opportunities for rehabilitating or replacing deteriorating distribution system infrastructure may want to explore financing programs like the USEPA’s Water Infrastructure Finance and Innovation Act program as well as the Drinking Water State Revolving Fund.