What it is
Clostridium perfringens is a bacterium from the gut of people and animals. It forms spores that survive heat, disinfection and long periods in water and soil, so it can reveal faecal contamination that other indicators have missed or that happened weeks ago.
Where it comes from
The sources are the same as for E. coli: sewage, septic systems, slurry and livestock, reaching the supply through an unprotected source, a damaged tank, or surface water after heavy rain. Its persistence means it can also appear when the original contamination has cleared.
Why it matters
Finding it means organisms from faeces have reached the water and that hardy ones, including parasites such as Cryptosporidium, might have too. Water should be boiled before drinking until the cause is found and a retest is clear. It is part of the Scottish new-build set for this reason.
What can be done about it
Close the route in, clean and disinfect the system, and fit protection that deals with spores: fine filtration (1 micron or better) ahead of UV disinfection, since UV alone is less effective against spores than against ordinary bacteria.
Information last reviewed 5 October 2026 by Pozzani Pure Water.