Value of legal and alternative regrowth parameters

The regrowth of microorganisms during the distribution of drinking water can lead to a number of problematic situations. Water companies therefore monitor drinking water quality very closely. Because of possible risks and problems for consumers, the Dutch Decree on Water Quality establishes parameters which describe the microbial water quality, and give an indication of the levels of microbial regrowth in the distribution system.

The objective of this project is (i) to find out whether the current legal parameters are still the most appropriate indicator parameters for regrowth and for the exposure of consumers to (pathogenic) microorganisms; and (ii) to research alternative and better biological parameters, which would be suitable indicators for regrowth and consumer exposure to (pathogenic) microorganisms in the drinking water distribution system.

Aeromonas, KG22 an alternative parameter

The activities involved are:

  • Consultations between the drinking water sector and government regarding the parameters Aeromonas and KG22 (the number of heterotrophic bacteria that can grow in a relatively rich agar medium at 22oC) in distributed drinking water, and what it is they indicate.
  • Determination of the value of Aeromonas and KG22 as regrowth and exposure parameters.
  • Development of an alternative parameter for  regrowth and exposure using a quantitative PCR method.
  • Data elaboration, reports, publication and congress.

Insight into the value of current parameters for the detection of regrowth problems

The project’s results provide insight into the value of current legal and of non-legal parameters in the detection of possible problems caused by regrowth in the distribution system. Alternative parameters, which better describe the level of regrowth in the drinking water in relation to possible problems, ensure that the ‘real’ problem locations are tackled, and thereby free the water companies from having to take unnecessary measures aimed at bringing (only) Aeromonas under control.

If it appears that the current legal parameters perform worse than one or several alternative parameters, the project’s information would be used to start discussions about possible modifications to the legal parameters for regrowth/exposure. For water companies, it would be desirable to modify the legal framework from one using several parameters for microbial quality and regrowth, to one using a single parameter. This would reduce the costs of the legal measurement programme. One possible outcome of this discussion is the incorporation into the law of more suitable parameters for regrowth/exposure, and thus also into the water companies’ measurement programmes.