What it is
The colony count at 37°C counts bacteria that grow at human body temperature over 48 hours. Compared with the 22°C count, it leans towards organisms that are more likely to be of animal or human origin, though most are still harmless environmental bacteria.
Where it comes from
Counts rise in warm, stagnant water, in tanks and dead legs, where biofilm has built up, and when filters or UV units are overdue for service. A sudden rise can follow contamination of the source.
Why it matters
There is no health-based limit and the guideline is no abnormal change. The 37°C count is a sensitive indicator: a jump in it, especially with a stable 22°C count, prompts a closer look at the coliform and E. coli results and at the condition of the system.
What can be done about it
As for the 22°C count: flush, clean and disinfect tanks and little-used outlets, service treatment equipment, and remove dead legs. UV disinfection after filtration protects against recurrence.
Information last reviewed 5 October 2026 by Pozzani Pure Water.