As offices, schools, health clubs, restaurants, hotels, and other facilities gradually reopen after shutdowns related to the COVID-19 pandemic, the public may confront yet another unmitigated health hazard: unsafe water from dormant or underused water systems. Because many buildings have sat unoccupied for months, disinfectants—such as chlorine—added by water utilities may dissipate in plumbing systems, increasing the risk for unchecked growth of disease-causing species of Legionella and other pathogenic bacteria. For water treated with chlorine, a concentration of 0.5 parts per million (ppm) of free chlorine is needed in order to be effective against Legionella and other bacteria. Free chlorine in dormant water systems would dissipate below 0.5 ppm in about 14 days by reacting with contaminants, such as microorganisms or organic compounds in the water, as well by reacting with water-pipe walls. Legionella can cause a type of pneumonia known as Legionnaires' disease when people inhale small droplets of water in air that contains the bacteria. In addition, algae, which is a food source for Legionella, can reproduce in stagnant water within storage or hot-water tanks during summer months, increasing the probability of exponential bacterial growth. See also: Bacteria; Bacterial growth; Chlorine; Coronavirus; Legionnaires' disease; Novel coronavirus is declared a global pandemic; Pathogen; Water treatment
Prolonged shutdown of large numbers of commercial buildings on a global scale is unprecedented. As a result, reopening guidelines were largely nonexistent. Recently, the U. S. Centers for Disease Control and Prevention (CDC) provided guidance to minimize Legionella risk before reopening businesses or buildings. At the same time, the U.S. Environmental Protection Agency (EPA) issued a checklist for restoring water quality before reopening buildings. Some U.S. states also have provided recommendations for returning dormant buildings’ water systems to service. All of these documents recommend frequent flushing of water systems, which is the responsibility of building owners and operators, as well as changing filters and cleaning all devices connected to plumbing systems, such as faucet aerators, shower heads, water coolers, and ice machines, which are the responsibility of the occupying tenants. After completing all of the control and remediation measures, testing for Legionella is needed to ensure safety. See also: Buildings; Public health
Before flushing a building’s water-supply system, building owners should be certain that the water entering the building is also not stagnant, according to civil and environmental engineering professor Andrew Whelton of the Center for Plumbing Safety at Perdue University in Indiana. Unless a city’s water utility has been flushing out the pipes beneath its streets, it is possible that—because of lowered water use in the commercial districts of that city—the water in those pipes is not fresh, Whelton said. He also recommends that building owners coordinate their flushing operations with local water authorities, which is important for preventing low water pressure or depressurization should too many buildings be using large amounts of water at the same time. Building owners and sewer authorities should also coordinate, because excessive simultaneous flushing from multiple buildings might produce a volume of discharge water that could overwhelm the capacity of a wastewater treatment plant. See also: Sewage collection systems; Sewage treatment; Water supply engineering
