29 days you can't see: the gap in monthly Legionella checks
A monthly check proves one minute. The risk has the rest of the month.
The standard legionella check is monthly. A technician runs the tap, reads the temperature, writes it down and signs the sheet. For that minute, the outlet is compliant.
The reading proves one minute. The risk lives in the rest of the month.
What the gap looks like
Legionella grows between roughly 20 and 45 degrees. If a hot outlet drifts below 50, or a cold one creeps above 20, for days between checks — a failing mixing valve, a boiler cycling wrong — the bacteria get their window. The monthly sheet still reads pass, because the reading happened on a good minute.
Why the snapshot persists
It is simply what a clipboard can do. One person cannot stand at every outlet all month. So the method takes a sample and hopes the sample is representative of the other twenty-nine days.
Closing the gap
Continuous per-outlet temperature turns the monthly snapshot into an unbroken line. A sustained drop is flagged the day it happens, not at the next visit. The pass or fail the regime wants is still there — it is now true for every minute, not one.
The point
A monthly check is a photograph of a moving thing. The temperature that fails is rarely the temperature you measured. Watch the outlet continuously, and the twenty-nine days stop being a blind spot.