What Happens When a Building Sits Quiet All Summer?
Key Takeaways
- Reduced occupancy changes water quality. When fixtures sit unused, disinfectant residuals decline and stagnant water can develop conditions that support bacterial growth.
- Stagnation alone isn't the problem — introduction is. Legionella risk increases when stagnant conditions are combined with the bacteria actually entering the plumbing system.
- Any building can have vacant zones. Even fully occupied buildings often have wings, floors, or individual fixtures that go unused for extended stretches.
- Recommissioning is a process, not a single task. Flushing lines, verifying hot water temperatures, and servicing water heaters all need to happen before reopening — not just one of them.
- Proactive management beats reactive response. CDC and ASHRAE guidance exists because prevention is easier, cheaper, and safer than responding to an outbreak after the fact.
The Hidden Water System Risks During Vacant Periods
When we think about preparing a building for summer—or getting it ready for occupants to return—our attention often goes to the obvious items. HVAC maintenance, landscaping, roof inspections, and general housekeeping are all important. But one of the most significant seasonal changes happens behind the walls, hidden from view.
It’s the building’s water system.
Whether it’s a school during summer break, a university residence hall, an office with hybrid schedules, or a seasonal facility, reduced occupancy changes how water moves through a building. Fixtures are used less frequently, water remains in plumbing longer, and the conditions inside the system begin to change.
That doesn’t automatically create a problem, but it does create conditions that deserve attention.
Buildings Most Likely to Experience Seasonal Low Water Use
Many facilities experience predictable periods of reduced occupancy throughout the year, including:
– K–12 schools during summer break
– Colleges and universities between semesters
– Office buildings with hybrid or seasonal staffing
– Hotels and resorts during slower travel periods
– Community centers and churches
– Seasonal recreational facilities
Even buildings that remain open may have wings, floors, or individual fixtures that see little or no use for extended periods.
Why Water Stagnation Matters
Building water systems are designed with the expectation that water will move regularly. As occupants use sinks, showers, drinking fountains, and other fixtures, fresh water enters the system while older water moves out.
When usage drops for days or weeks at a time, water can become stagnant. During this period, disinfectant residuals may decline, water temperatures can move into ranges that support microbial growth, and biofilms—the thin layers of microorganisms that naturally develop on pipe surfaces—can become more established.
These changes can create favorable conditions for bacteria, including -Legionella-, the organism responsible for Legionnaires’ disease.
It’s important to remember that stagnant water alone doesn’t mean -Legionella- is present. However, prolonged low water use is one of several factors that can increase risk if the bacteria are introduced into a building’s plumbing system.
Preparing for Reopening
Before occupants return, it’s worth taking a proactive approach to recommissioning the building’s water system.
Depending on the building and its water management program, that may include:
– Flushing hot and cold water lines to replace stagnant water with fresh water.
– Running infrequently used fixtures, including sinks, showers, drinking fountains, and hose bibs.
– Verifying that hot water systems are maintaining appropriate temperatures.
– Inspecting and servicing equipment associated with the water system, such as water heaters and storage tanks.
– Reviewing the building’s water management plan to ensure recommended procedures have been completed.
– Considering environmental sampling when appropriate as part of a broader risk management strategy.
These measures can help restore normal water quality conditions before the building returns to full occupancy.
Prevention Is Always Easier Than Response
Legionnaires’ disease is uncommon, but outbreaks can have serious consequences for building owners, occupants, and public health. That’s why organizations such as the CDC and ASHRAE emphasize proactive water management rather than waiting for a problem to develop.
For facility managers and property owners, the goal isn’t to create unnecessary concern. It’s to recognize that seasonal changes in occupancy affect more than energy use or maintenance schedules—they also influence the building’s water system.
A little preparation before reopening can go a long way toward protecting building occupants and supporting a healthier indoor environment.
As summer progresses and facilities prepare for students, employees, residents, or guests to return, don’t overlook the plumbing system that’s been quietly waiting behind the scenes. Giving it the attention it deserves today may help prevent much larger challenges tomorrow.
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Jeremy Westcott
Jeremy Westcott is Managing Director at Environmental Testing & Consulting, Inc., and a trusted advisor to contractors and facility managers on environmental compliance and enforcement.