What is biofilm?

The inside of a water mains pipe is often covered with a slimy layer. This layer is known as biofilm. Biofilm comes into being as a result of the attachment and growth of micro-organisms in the mains surface. For this purpose they use nutrients that are naturally present in water, even in drinking water. The most important nutrients are assimilable organic carbon compounds, nitrogen and phosphorus.

Biofilm is often found in the water pipes of hospitals, rest and nursing homes, as well as in the water mains of companies …. Biofilm is dangerous. It provides shelter to micro-organisms, and the presence of nutrients can induce an explosive growth. Legionella pneumophila (the originator of the highly feared Legionnaires' disease) is, besides many other micro-organisms, a typical resident of this biofilm.

The speed at which biofilm is formed is, among other things, affected by the materials used for the pipes, the holding time of the system and the temperature of the water. In addition, the temperature of cold, stagnant water in the mains may also be affected by the ambient temperature. Water temperature ranging from 25 to 45 °C for cold water is eminently possible (e.g. in the summer months) and is one of the best possible stimulus for the growth of many micro-organisms.