How do you protect plumbing in a vacant commercial building?

CDC says "stagnant or standing water in a plumbing system can increase risk for growth and spread of Legionella and other biofilm-associated bacteria." It adds that in stagnant water, hot water temperatures can fall into the Legionella growth range of 77 to 113 degrees Fahrenheit. CDC also says a prolonged period may mean weeks or months, depending on the plumbing, disinfectant levels, water heater settings and water use.

Standing water also corrodes pipe. CDC says corrosion during long periods of low or no water use can lead to potentially high levels of lead or other metals in a building's drinking water.

EPA recommends that owners of buildings with low or no use flush the plumbing regularly. Its steps: flush the service line from the main to the building first, then work from the point where water enters toward the farthest tap, running cold water before hot, and run hot water until it reaches its maximum temperature. That includes toilets, drinking fountains and ice makers.

How often? CDC's potable water guidance says to flush low-flow piping runs and dead legs at least weekly. That guidance is written for occupied buildings with a water management program, so treat it as a benchmark, not a rule for your building. Write down each round. Our page on Legionella water management plans in Phoenix covers who needs a formal plan.

Every fixture and floor drain has a trap, a U-bend that holds water and blocks sewer gas. Empty rooms mean those drains never get water, and the seal can dry out. CDC lists "sewer gases that enter buildings through dry sanitary sewer drain traps" among the hazards of a shutdown. EPA's advice is to fill all drain traps with water. A floor drain that will sit dry for months may need a trap primer; see do commercial floor drains need a trap primer.

The two agencies point at different moments. EPA says to keep the water heater at or above 140 degrees Fahrenheit while a building is closed, per CDC guidance, and CDC's reopening steps say to make sure it is set to at least 140. EPA also says to drain and clean hot water heaters, following the manufacturer's instructions, when preparing to reopen after weeks or months of stagnation, and CDC says to determine whether the manufacturer recommends draining after a prolonged period of disuse. So the answer depends on how long the building will sit. For a long vacancy, check the manufacturer's instructions for which path applies. See turning off a water heater on vacation.

Closing the main shutoff means a cut pipe has nothing behind it. Leave any valve that feeds fire protection alone and ask your fire protection company before closing anything. Church Mutual, an insurer, lists plumbing pipes among the copper thieves seek and warns that "free-flowing water from damaged or stolen plumbing can instantly turn into a major restoration project." It also reports repeat thefts after repairs. Lock the utility rooms and check the building often.

Backflow assemblies stay on the list. Phoenix City Code 37-144 puts the duty to test assemblies at least once a year on the customer, the person with "physical control, authority or responsibility for a water system that receives water service from the City public water system," and the Director may require more frequent testing. See who can test backflow assemblies in Arizona.

Phoenix City Code requires owners to register nonresidential properties on the vacant property registry if they are vacant for 30 or more days, and to be reachable by phone or text within 30 minutes of a request from police, firefighters, or code enforcement. Neighborhood Services decides whether your building qualifies.

HQ does commercial plumbing and is licensed and insured. We can check shutoffs, water heaters and traps, with a free estimate and upfront pricing. 24/7 emergency service is there if a vacant building floods. Read planning a commercial water shutoff before you close anything off.