Environmental Science and Research (ESR) is undertaking a scientific study to identify whether viruses are present in groundwater in Canterbury
The research has been commissioned by the Water Services Authority - Taumata Arowai and is being undertaken in collaboration with Christchurch City Council and Environment Canterbury.
The aim of this study
The main indicator of bacterial quality of drinking water is E. coli. When E. coli are found it is an indication of faecal contamination and that drinking water may not be safe to drink. But the characteristics of bacteria are different to other groups of organisms like protozoa and viruses.
For example E. coli may survive for hours in the natural environment, but viruses can survive for months and, in some cases, years. Protozoa can form cysts or oocysts when exposed to the environment making them very hardy and resistant to the things that would kill bacteria. So, while the presence of E. coli is a good indicator of bacterial contamination, it is not a good indicator of viral or protozoal contamination.
We know viruses can be found in surface water. However, we don’t know if viruses that can impact human health (for example norovirus) are present in groundwater.
This research seeks to identify if viruses are present in groundwater that is typically used for drinking water supply.
The project also seeks to identify a simple indicator of virus contamination, in the way that E. coli is used to indicate bacterial contamination.
Why we’re conducting this study
In 2025 we’ll review New Zealand’s Drinking Water Quality Rules (the Rules) for supplies that serve more than 500 people (large supplies). This scientific study is being undertaken to inform this review.
Currently the bacterial Rules provide drinking water suppliers with the option of using chlorine as a primary disinfectant. If suppliers use this option, the Rules also require them to retain the water for a specific period to provide chlorine contact time to ensure bacteria and viruses are killed before that water is provided to consumers. Though this Rule is in the bacterial compliance section, it is primarily intended to control viruses as control of bacteria requires very little chlorine contact time.
If this study finds viruses aren’t present in groundwater, we may decide to consult on a potential adjustment of chlorine rules for groundwater sources that meet well defined conditions as part of the Rules review for large supplies.
It’s possible that further research and analysis will be required before we can determine whether any changes to the Rules are justified, and if so to identify options.
If the Rules are updated, any changes are unlikely to take effect for suppliers before 2026 at the very earliest. If changes are made, it is anticipated that supplies that meet current chlorine contact time Rules for bacterial compliance would also meet any potential virus compliance rules without making any significant changes to their supply.
We must emphasise that we don’t know what the findings of this scientific study will be or what, if any, effect this research could have on the Rules.
It’s also critical to highlight that any potential changes to Rules would not impact residual disinfection requirements for reticulated networks. These will remain in place to protect drinking water as it travels from the treatment plant to consumers’ taps.
Timeline
This study is currently expected to run until June 2025. We will update our website information as the study progresses.