When it comes to water management, ensuring high-quality drinking water is critical. Norrvatten, one of Sweden’s largest water producers, has established guidelines to determine and address abnormal changes regarding cultivable microorganisms by endorsing the flow cytometry method. Norrvatten's guidelines are developed in response to the Swedish National Food Agency's new regulations on drinking water (LIVSFS 2022:12) that came into force in January 2023. Let’s delve further into Norrvatten’s guidelines as we shed light on the critical aspects of their approach.
Cultivable microorganisms and water quality
Understanding the background of cultivable microorganisms is crucial. The HPC (heterotrophic plate count) analysis method, measuring bacterial colonies on culture media, has been a traditional indicator of water quality. However, interpreting these results requires considering factors such as temperature, nutrient levels, and the absence of disinfection.
1. Changes in regulations
Recent regulation changes, such as LIVSFS 2022:12 by the Swedish National Food Agency, have shifted the focus from specific limits to evaluating whether “no abnormal change” has occurred. These changes necessitate new methods for interpreting and determining abnormal changes in water quality.
It follows the recent change in EU drinking water legislation, the Drinking Water Directive, and the trend of other countries, such as Switzerland, where the SVGW (the Swiss Association for Gas and Water) also endorsed this method.
2. Shift in international standards
The recent paradigm shift in assessing heterotrophic bacteria in drinking water extends beyond health considerations, reflecting a nuanced perspective. Traditional methods for quantification of bacteria in water (HPC) detect only between 0.01-1% in a sample and have a lag measure of 3 days (68+/-4h). Flow cytometry enables the enumeration of >99% of the bacterial population. Some municipalities have successfully used flow cytometry, both lab-based and online, to monitor, visualise and manage bacterial risk in potable water. This prompts a reevaluation of measurement approaches, moving away from conventional methodologies.
Simultaneously, the water industry witnesses transformative changes propelled by the new EU Directive on the quality of water intended for human consumption. Driven by the first-ever approved European Citizens’ Initiative Right2Water, this directive ushers in stringent monitoring procedures to safeguard potable water as a precious resource. It advocates for a more systemic use of technologies for continuous water quality monitoring. It introduces a risk-based approach, emphasising a risk management system to control processes along the entire supply chain.
Notably, the revised directive omits mentioning a Colony-Forming Unit (CFU) value for the total plate count. Instead, it emphasises vigilance for abnormal changes, aligning with a more dynamic and proactive stance in water quality management.
Norrvatten’s current situation
Norrvatten collated and summarised the results from all pumping stations across the area to get an overview of the degree of variation. Analyses of 3-day cultivable microorganisms from pumping stations between 2015 and 2023 showed variations, with some stations exhibiting higher growth concentrations. The results were used to calculate variation and alarm values for each station to enable the Norrvatten microbiologists to determine if there is an increasing trend.
Norrvatten reviewed previous data to assess normal and abnormal changes in microbial levels before commissioning new pipes. Under the old guidance, pipes were often flushed for several months before the guideline HPC values were reached, adding to the total cost of commissioning and wasting large amounts of treated water. Referring to studies showing that HPC culture testing may not accurately assess the microbial risks, Norrvatten started using flow cytometry together with HPC to get a better overall picture.
The flow cytometry fingerprint includes the total number of microbial cells and the distribution between cells with high nucleic acid content and those with low DNA content. This shows how closely the water in the new pipeline matches the plant's. Therefore, a new pipeline could be approved when the fingerprint matches or when there is a downward trend in cell numbers.
Norrvatten guidelines for cultivable microorganisms
To adhere to the evolving regulatory demands, Norrvatten established new guidelines. In their report, microbiologists Linda Holmer and Mikael Danielsson emphasise the importance of adhering to specific parameters to maintain water quality. The focus is on compliance with no abnormal change to cultivable microorganisms.
Alarm limits and monitoring
Norrvatten used their heterotrophic plate count (HPC) historical data to determine normal values and calculate alarm limits for each pumping station and reservoir. Values exceeding the action level trigger an alarm, prompting a thorough investigation to assess the need for corrective action.
Flow cytometric baselines
Norrvatten is now establishing flow cytometric baselines for bacterial counts to enhance monitoring within the distribution network. Pumping stations and reservoirs serve as references. This approach ensures a comprehensive evaluation of water quality trends and facilitates comparisons in different scenarios.
Commissioning new pipelines
Norrvatten employs a comparative analysis using flow cytometric fingerprints and culture tests when commissioning new pipelines or after maintenance work. Samples are taken from incoming and outgoing water from the new section, allowing for a detailed examination of water quality changes. This method optimises the evaluation process and aids in decision-making regarding pipeline readiness for operation.
Future directions and conclusion
Norrvatten envisions a future where flow cytometric analysis precedes traditional cultivation methods. Plans include analysing almost all water samples using flow cytometry to establish baselines for the entire distribution area. The emphasis will be on trends rather than concentrations, aligning with the evolving landscape of water quality analysis.
In conclusion, Norrvatten’s proactive guidelines and innovative approaches ensure a vigilant stance on water quality. By integrating advanced technologies like flow cytometry and adapting to changing regulations, Norrvatten remains at the forefront of maintaining safe and reliable drinking water for its communities.
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For more detailed information, refer to the original Norrvatten guidelines report. Please note that it’s only available in Swedish.
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