Fast alternative for the heterotrophic plate count at 22°C (HPC22) following interventions in the drinking water distribution system

Interest and objective

Following maintenance activities or pipe breaks in the distribution system, there is a risk that external microorganisms end up in the drinking water, leading to the possibility that customers will no longer be supplied with water of impeccable quality. The intrusion of these microorganisms – particularly faecal pathogens – from the surrounding environment therefore needs to be prevented. Between 0 and 24 hours following the maintenance activities, water samples are taken to control for Escherichia coli, enterococci, coliform bacteria and HPC22 (Meerkerk, 2021). HPC22 is currently the slowest method of assessing microbial water quality following interventions and calamities (e.g. pipe breaks), since the samples have to be incubated for three days in an agar culture medium at 22°C. There are other general microbial water quality parameters available besides HPC22 (e.g. total bacterial cell numbers, ATP concentration, enzyme activity, using sensors (BACTcontrol and ColiMinder)), which produce a result relatively quickly. How suitable one or several of these parameters is as an alternative to HPC22 following maintenance activities or pipe breaks is however still not clear. The objective of the project is to determine whether alternative parameters can measure possible microbial anomalies in drinking water following maintenance activities or pipe breaks, in a manner that is faster, and of equal or superior sensitivity, when compared to HPC22.

Activities

During the first project phase criteria will be defined that the alternative parameter must meet and upon which it will be scored (including reliability, accuracy, detection limit, applicability and rapidity). The practical aspects of the different methods will then be examined (including laboratory implementability, costs, field implementation and mobile online techniques). On the basis of these criteria, at the end of the project, it will be determined which methods are suitable alternatives to HPC22.
In the second phase different methods will be tested and compared to HPC22. Artificially produced contaminated drinking waters will be measured using the different analytical methods. To this end, dilutions will be made from groundwater, surface water, rainwater and soil material in different drinking water types. Thus, different contamination scenarios that can arise during maintenance activities and pipe breaks will be simulated.
In the third phase the methods will be compared to each other using water samples taken in practice following maintenance activities and/or pipe breaks. Water samples will be taken immediately following the activities and up to a few hours or days afterwards, and analysed using each of the methods.

Anticipated results and application

The objective of the project is to discover for the drinking water utilities whether there are methods available, that are faster and more sensitive than the HPC22, to identify anomalies in the microbial water quality following maintenance activities or pipe breaks in the distribution system.

Outputs:

1. Criteria that an alternative parameter to HPC22 must satisfy.
2. Alternative microbial parameter to HPC22 (e.g., ATP, cell numbers, enzyme activity), with which to determine anomalies in the microbial water quality following maintenance activities or pipe breaks in a manner that is faster and more sensitive.