When thinking about water quality, treatment process are a focal point for ensuring water safety. While treatment processes are a major component of delivering safe water, it is important to remember that treatment is but one component in an integrated system for delivering safe water to customers.
The reticulation network serves two main purposes in a drinking water supply system:
• Transport of water within the network
• Acting as a protective barrier against the ingress of pathogens and contaminants into the network.
The role of providing a protective barrier is crucial to maintaining water safety, as chlorine residual within the network is often not sufficient to provide protection against microbial hazards entering the supply, particularly for protozoan pathogens.
A key step in ensuring hygiene in a drinking water supply is to correct hygiene during repairs and maintenance. Repairs of mains and services are an important part of maintaining a drinking water supply system. Even the best managed reticulation networks will invariably require repairs, while renewal of mains and services and the installation of new areas of the network is an ongoing activity for all supply systems.
Microbial hazard during network maintenance is largely caused by contamination of pipework and fittings either before or during works. When developing procedures and training technicians, it is important to consider contamination risks throughout the process. When considering the process, ensure that a hygienic 'chain of custody' is maintained. Key questions for assessing preparation for works include:
• Are the materials, including seals and lubricants, suitable for drinking water service?
• How are materials delivered?
• Are pipework and fittings sealed during transport and storage?
• How are material stored?
• Are there any cross contamination risks from materials used in sewer systems?
• How are materials protected during transit to the work site?
• What processes are in place to disinfect materials prior to installation?
During the maintenance works, it is important to consider the potential sources of contamination and ensure that appropriate controls are in place. Segregation of tools and equipment used for sewer works, disinfection of tools and materials prior to installation, dewatering of work sites, the use of pipe stands and clean work areas all contribute to the maintenance of hygiene during repairs and installation of new services.
It is also worth considering whether works can be conducted under pressure. Works conducted under pressure reduce the likelihood of infection from ingress of water from the work site, however this is often only suitable for small repairs.
On completion of the repair, it is important to verify the integrity of the repair using pressure testing. Leaks in the network are not just water lost, but represent a potential vector for ingress into the reticulation network. Where possible, exposed pressure testing will provide greater opportunity to identify failure of joints and seals. Where pressure testing is conducted on buried services, additional attention is required to ensure that filling of the service removes all air from the pipework and does not provide a false-positive result for pressure based integrity testing.
Once the integrity of the repair is confirmed, thorough flushing is required. Flushing should consider an appropriate order of de-isolation and selection of hydrants or other points for flushing to ensure that potentially contaminated water is not supplied to customers. Sufficient flow and volume is required to ensure that pipework is fully flushed. The presence of an appropriate free chlorine residual should be confirmed prior to completion of the flush.
For assistance in developing hygienic work practices for network maintenance, don't hesitate to contact Viridis.