CFU – Colony Forming Units – is an indiacator of the amount of living microorganism in a liquid. This figure describes the number of bacteria or fungi that live and multiply in water over a certain period of time. It is necessary to consider a period of time, as a single bacterium can quickly become a whole colony. The measured value of only one point in time cannot give any information about the actual amount of microorganisms. To ensure comparability, these bacterial counts are always referred to 100 ml or one litre.
drinking water ordinance
Bacteria or fungi in drinking water can endanger the health of the consumer and are therefore strictly monitored. This applies not only to drinking water, but also to cooling water, for example.
There are therefore corresponding regulations at national or European level, where the permitted limit values for the respective waters are described. The German Drinking Water Ordinance is based on the EU Drinking Water Directive and the Infection Control Act.
drinking water sampling
How the sampling must be carried out is also regulated in the Drinking Water Ordinance. Sampling and analysis must be carried out by a certified body. The water sample is placed in a Petri dish. If a high quantity of microorganisms is to be expected, the water sample can also be diluted. After a certain period under standardized conditions, the number of CFUs in the water can be calculated.
The result is given in CFU/l. Values above 100 CFU/100 ml are not permitted for drinking water, cooling water should contain less than 10,000 CFU/100 ml.
These limits are set and controlled by the state authorities. As there is no uniform international standard, the values may vary from country to country.