Institute of Environment, Health and Societies, Brunel University London, Uxbridge, Middlesex, United Kingdom.
Aqua Technologies Europe Ltd, Hounslow, Middlesex, United Kingdom.
PLoS One. 2018 Apr 12;13(4):e0195635. doi: 10.1371/journal.pone.0195635. eCollection 2018.
Water-borne bacteria, found in cold water storage tanks, are causative agents for various human infections and diseases including Legionnaires' disease. Consequently, regular microbiological monitoring of tank water is undertaken as part of the regulatory framework used to control pathogenic bacteria. A key assumption is that a small volume of water taken from under the ball valve (where there is easy access to the stored water) will be representative of the entire tank. To test the reliability of this measure, domestic water samples taken from different locations of selected tanks in London properties between November 2015 and July 2016 were analysed for TVCs, Pseudomonas and Legionella at an accredited laboratory, according to regulatory requirements. Out of ~6000 tanks surveyed, only 15 were selected based on the ability to take a water sample from the normal sampling hatch (located above the ball valve) and from the far end of the tank (usually requiring disassembly of the tank lid with risk of structural damage), and permission being granted by the site manager to undertake the additional investigation and sampling. Despite seasonal differences in water temperature, we found 100% compliance at the ball valve end. In contrast, 40% of the tanks exceeded the regulatory threshold for temperature at the far end of the tank in the summer months. Consequently, 20% of the tanks surveyed failed to trigger appropriate regulatory action based on microbiological analyses of the water sample taken under the ball valve compared to the far end sample using present-day standards. These data show that typical water samples collected for routine monitoring may often underestimate the microbiological status of the water entering the building, thereby increasing the risk of exposure to water bourne pathogens with potential public health implications. We propose that water storage tanks should be redesigned to allow access to the far end of tanks for routine monitoring purposes, and that water samples used to ascertain the regulatory compliance of stored water in tanks should be taken at the point at which water is abstracted for use in the building.
水中细菌存在于冷水储水箱中，是引起各种人类感染和疾病的病原体，包括军团病。因此，作为控制病原菌的监管框架的一部分，定期对水箱水进行微生物监测。一个关键假设是，从小球阀下方（容易接触到储存水的地方）取一小部分水，就可以代表整个水箱。为了测试这一措施的可靠性，根据监管要求，对 2015 年 11 月至 2016 年 7 月期间从伦敦物业的选定水箱的不同位置采集的家用水样进行了总需氧量（TVC）、假单胞菌和军团菌的分析，分析工作在认可实验室进行。在调查的约 6000 个水箱中，只有 15 个是根据从正常采样舱（位于球阀上方）和水箱末端（通常需要拆卸水箱盖，有结构损坏风险）采集水样的能力选择的，并且获得了现场管理人员的许可，允许进行额外的调查和采样。尽管水温存在季节性差异，但我们在球阀末端发现 100%符合规定。相比之下，在夏季，40%的水箱在水箱末端的温度超过了监管阈值。因此，根据现行标准，与从水箱末端采集的水样相比，通过在球阀下采集的水样进行微生物分析，有 20%的水箱未能触发适当的监管行动。这些数据表明，为常规监测而采集的典型水样通常可能低估了进入建筑物的水的微生物状况，从而增加了暴露于水源病原体的风险，这可能对公众健康产生影响。我们建议对水箱进行重新设计，以便能够在常规监测目的下进入水箱末端，并应在建筑物中抽取用于确定水箱中储存水的监管合规性的水样。
