By Kelly A. Reynolds, MSPH, PhD
The municipal drinking-water distribution system is a complex delivery network designed to provide adequate potable water needs to entire communities. Much information has been published relative to concerns of the distribution system integrity and ability to provide safe, consistent water to consumers. Needs for infrastructure improvements, rapid response to main breaks and leaks, biofilm control and preventing intrusion events, dead legs and pressure losses, are just some of the prevalent water quality delivery issues. Less common are discussions around safe water storage prior to delivery. Although industry standards and guidelines exist, maintaining water quality over prolonged storage presents additional challenges and uncertainties for end users.
Storage failures
Water storage systems are designed to balance volume demands and manage pressure differentials in the distribution system. They also serve as back-up reservoirs for fire suppression or emergency water needs. Poor management of the age and adequate mixing of stored water supplies may lead to significant problems, including increased microbial growth and chemical changes (see Table 1).
The majority of tanks are either elevated or ground storage reservoirs. Ground storage tanks could be below ground, partially buried or fully above ground and may or may not be covered. Birds and insects can transmit microbial pathogens to storage tanks without covers or with poor seals. Sanitary surveys have revealed up to a 25 percent rate (n=60-75 inspected tanks annually) of “serious sanitary defects” during annual tank inspections in some regions, leading to increased bacterial counts along the distribution system.2 Salmonella, Campylobacter, Vibrio and Cryptosporidium are just a few of the microbial pathogens carried by birds and waterfowl. Several have also been associated with drinking-water outbreaks linked back to unsanitary storage conditions.
Failures of varying degrees have made media headlines, reducing consumer confidence in quality delivery. According to several local New York City media outlets, including City & State, New York and Fox 5 News, the New York City Housing Authority’s Annual Roof Tank Inspection Reports showed evidence of significant sanitary violations where wooden water storage tanks were contaminated with animals and insects.3,4 Residents who could afford it purchased bottled water due to tap water that was “too dark, ugly” to consume.
Storage tanks may also provide a source of insecurity as an entry point for potential intrusion via acts of vandalism or terrorism. The variability of design, conditions, security and maintenance creates a complex scenario of possible exposure to drinking-water contaminants from the approximately 154,000 finished water storage facilities in the US.5
Monitoring and inspection needs
Increased turbidity, warm water and foul taste and odor are potentially serious indicators of storage tank problems at the point of consumption. Ideally, problems should be identified prior to consumer reports of changing aesthetics. Routine monitoring and inspection can be used to identify problems early. Lowered disinfectant residual, increased DBP levels, elevated bacterial counts and increased nitrite/nitrate levels are examples of indicators where a corrective action may be needed. Appropriate inspection, water circulation and cleaning are imperative for safety. Quality can be impacted by source-water conditions and treatment, tank maintenance plans, materials and age of system, hydraulics and design and even temperature or climatic conditions. Tanks should be inspected regularly by an industry professional to make sure there are no problems with the interior or exterior structure or overall sanitary integrity.
Inspection of overall tank condition as well as any unprotected openings (evident by leaks or incoming light) are standard observations that should occur every one to four months. Further, observation of covers, seals, overflow or air vents, screens, access hatches, drains and any foreign blockage (sediment, debris, corrosion, insects, leaves or animal carcasses) should be part of an inspection checklist. Inspections may involve completely emptying the tank or keeping the tank full and using a submergible, remotely operated camera to visualize interior structures. Corrective actions are needed should significant deficiencies be identified. Tanks should be washed out at least every three years and more often when source supplies have a history of sediment problems. Measuring the depth of sediment during routine inspections can provide a record of changes over time and help with making decisions for cleaning frequency.
Regulatory radar
According to a 2003 US EPA survey, of the $277 billion needed over the next 20 years for drinking-water infrastructure improvements, approximately $25 billion is targeted for storage project needs.6 How these investments will be prioritized is not clear or consistent across states. In addition, states’ directives on required maintenance, comprehensive inspection and cleaning frequencies are highly varied and even self-directed by local utilities.
There are no specific federal regulations for water quality monitoring or inspection of storage facilities. US EPA, however, provides a guidance on how to inspect and clean finished water storage tanks.1 Around 2002, a series of white papers were published as a resource to US EPA in anticipation of a Total Coliform Rule (TCR) revision that might include finished water storage tanks and other distribution system issues. In the 2013 final Revised TCR, however, storage tanks were not included for regulatory control. Most recently, the Director of US EPA’s Office of Groundwater and Drinking Water identified storage tanks as a top emerging issue still on the regulatory radar.7
Deficiency reports, the lack of an enforceable federal standard and a multitude of known vulnerabilities associated with finished storage facilities make a strong case for a final barrier of protection at the point of use of water consumption. Based on the published literature, few studies are currently focused on finished-water storage facilities, despite a list of concerns published in the 2002 reports to inform potential TCR revisions. Recent media headlines may have an impact on the prioritization of water quality assessments and controls for storage tanks in the future.
References
- AWWA. American Water Works Association for the EPA. Finished Water Storage Facilities. Washington, D.C.; 2002. https://www.epa.gov/sites/production/files/2015-09/documents/2007_05_18_disinfection_tcr_whitepaper_tcr_storage.pdf. Accessed August 14, 2018.
- LeChevallier MW. Conducting self-assessments under the revised Total Coliform Rule. 2014;106(9):90-102.
- Runyeon F. Inspectors reported contamination in water tanks. City & State, New York. https://www.cityandstateny.com/articles/politics/new-york-city/nycha-contamination-water-tanks. Published July 31, 2018.
- Arschin D. Contamination of NYCHA water tanks went unreported. 2018. www.fox5ny.com/news/nycha-water-tanks-contamination. Accessed August 15, 2018.
- National Research Council. Drinking Water Distribution Systems. Washington, D.C.: National Academies Press; 2006. doi:10.17226/11728
- AWWA. American Water Works Association for the EPA. Distribution System Inventory, Integrity and Water Quality Background and Disclaimer. 2007. Accessed August 14, 2018.
- Roberson JA. Thinking About Your Finished Water Storage Tanks. J Am Water Works Assoc. 2014;106(7):23-26. doi:10.5942/jawwa.2014.106.0101
About the author
Dr. Kelly A. Reynolds is a University of Arizona Professor at the College of Public Health; Chair of Community, Environment and Policy; Program Director of Environmental Health Sciences and prior, Director of Environment, Exposure Science and Risk Assessment Center (ESRAC). She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at [email protected]