Frequently asked questions about building water testing
The questions that come up most often, answered as briefly as they can honestly be answered, and, on the health questions, answered by pointing somewhere else, deliberately.
One thing before the questions
If your question is about somebody's health, it is not a question for this site. Contact your local or state health department and the clinicians involved. Everything below is about buildings and water systems.
Frequently asked
Does a negative result mean the building is safe?
No. It means the organism was not detected at those points, by that method, on that day. Safety is a property of a managed system over time, see what testing establishes.
Who is responsible for the building's water systems?
The owner or operator, with responsibilities frequently split in leased buildings. Settling that boundary in writing is a prerequisite to any workable sampling plan.
How often should we test?
At the frequency your programme sets, and at any frequency a requirement imposes, which for cooling towers is more often prescribed than for domestic water. No frequency is published here.
What limits should results be compared against?
Those in your programme or in the applicable requirement. This site publishes no thresholds or action levels, because a number quoted outside its framework is worse than no number.
Is a water management programme required for our building?
It depends on the building type, the systems present and the jurisdiction. [Applicable requirements to be cited before publication.] Where it is not required, it remains the framework testing is only meaningful inside.
Can we do the sampling ourselves?
Some programmes do, with training and a documented procedure. Collection technique affects results, so it is a decision to make deliberately, see sampling and analysis.
How long do results take?
It depends on the laboratory method, and the difference between approaches is substantial. Ask at bid stage, because turnaround changes how a result can be used.
What do we do if a result comes back high?
What your programme’s response plan says, which is why the plan is written before the sample is taken. Where illness is involved, public health authorities lead. This site interprets nothing.
Do cooling towers have separate rules?
In some jurisdictions, yes, registration, written plans, prescribed testing and reporting. The variation between places is larger here than anywhere else in this subject, see cooling towers.
We reopened after months of low occupancy. Where do we start?
With the programme and a flushing regime, then a baseline round if the programme calls for one. Low occupancy is one of the standard triggers to revisit everything.
Who takes the samples, and who analyses them?
We take the samples, and they are cultured in an accredited laboratory. What we do not do is interpret a result as a health matter or give advice about anyone’s health: we test water, not people, see how we work.
Last reviewed July 29, 2026.
Ask about a specific building
General answers only go so far. Tell us the systems and the programme status, and we will answer against your actual building.
Legionella Screen samples building water systems and cooling towers and has the samples analysed by culture in an accredited laboratory. It does not diagnose illness, does not treat anyone, and gives no medical advice of any kind.