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When water sits too long, hand-washing and flushing toilets can aerosolize bacteria-laden stagnant water.

Prolonged closures and lack of water flow can lead to dangerous concentration of pathogens and metals

When buildings stand virtually abandoned due to pandemic stay-at-home orders, water stops flowing through their plumbing and bad things start to happen inside the pipes. Harmful chemicals begin to build up and potentially pathogenic microorganisms start to grow. It takes only days for dangerous concentrations to form, but many buildings will remain closed for months. How serious might the problem become? There has been little authoritative information or guidance on water quality in vacant buildings until now, but a new Purdue University study has shed some light on the issue.

The National Science Foundation issued a Rapid Response Research grant to a Purdue research team to monitor building water quality while vacant and when they are again occupied. The study aids a national push to arm public health agencies, building owners, and water operators with information on how to start up buildings left vacant by the pandemic without risking human health. Purdue University environmental engineer Andrew Whelton explained:

We don’t design buildings to be shut down for months. This study focuses on the consequences and will help building owners make sure their buildings are safe and operational when occupants return.

Stagnant Water in Plumbing

While staying at home can help prevent COVID-19 transmission, stagnant water in water tanks, filters, heaters, and softeners can promote growth of the deadly Legionella bacterium that causes Legionnaires’ Disease, as well as other pathogenic bacteria. The researchers, however, also note that not all bacteria that might flourish in pipes are pathogenic, and not all danger is from pathogens.

Lead and copper in water can cause neurological and cardiovascular problems, as well as diarrhea and nausea. During normal use, the leaching of metals into the water from pipes is so slow that the concentrations are negligible at the point of use, but they can quickly reach dangerous levels if water sits too long in pipes.

Flushing toilets and hand-washing can aerosolize bacteria-laden stagnant water and cause lung disease. This vector of disease is active even if a water supply is chlorinated because disinfectants in water dissipate over time.

Keeping Water Moving

The United States (including some individual states), Canada, England, and Europe have made recommendations to keep water safe while buildings remain dormant during the COVID-19 pandemic. Although the recommendations differ, they agree that it’s important to not let water stagnate.

Faucets, water heaters, softeners, refrigerators, toilets, and other water system components like cooling towers should be flushed at least weekly to replace possibly bacteria-laden water with fresh, and to remove potentially dangerous sediment. The length of the building flush depends on unique conditions for each building, but a large building could require hours or even days to achieve a sufficient turnover of water.

A key strategy is to not let water sit in the first place. Once a problem develops, mitigation becomes problematic. Caitlin Proctor, a doctoral fellow at Purdue University, warned:

As we come back to work after social distancing, even complete building flushing might not be successful in drawing in fresh water.

Flushing a building after a problem has developed may require chemical shocking and personal protective equipment and, consequently, more expense.