Abstract：
Secondary water supply systems (SWSSs) are widely used to supply water to high-rise households in urban residential buildings. A special mode of double tanks with one used while another was spared was noted in SWSSs, which would facilitate microbial growth due to longer water stagnation in the spare tank. There are limited studies on the microbial risk of water samples in such SWSSs. In this study, the input water valves of the operational SWSSs consisting of double tanks were artificially closed and opened on time. Propidium monoazide-qPCR and high-throughput sequencing were performed to systematically investigate the microbial risks in water samples. After closing the tank input water valve, it may take several weeks to replace the bulk water in the spare tank. The residual chlorine concentration in the spare tank decreased by up to 85 % within 2-3 days compared with that in the input water. The microbial communities in the spare and used tank water samples clustered separately. High bacterial 16S rRNA gene abundance and pathogens-like sequences were detected in the spare tanks. Most antibiotic-resistant genes (11/15) in the spare tanks showed an increase in their relative abundance. Moreover, when both tanks within one SWSS were in use, the water quality of the used tank water samples deteriorated to varying degrees. Overall, running SWSSs with double tanks will reduce the replacement rate of water in one storage tank, and consumers who use taps served by the presented SWSSs may have a higher microbial risk.
摘要：
二次供水系统（SWSS）被广泛用于向城市住宅中的高层家庭供水。在SWSS中注意到了一种特殊的双坦克模式，其中一个使用而另一个幸免，由于备用罐中的水停滞时间较长，这将促进微生物生长。关于此类SWSS中水样的微生物风险的研究有限。在这项研究中,由双罐组成的操作SWSS的输入水阀被人工关闭并按时打开。进行了单叠氮丙啶qPCR和高通量测序，以系统地研究水样中的微生物风险。关闭水箱进水阀后，更换备用水箱中的散装水可能需要几周的时间。与输入水中相比，备用罐中的余氯浓度在2-3天内降低了高达85％。备用和使用过的水箱水样中的微生物群落分别成簇。在备用罐中检测到高细菌16SrRNA基因丰度和病原体样序列。备用罐中的大多数抗生素抗性基因(11/15)显示其相对丰度增加。此外，当一个SWSS中的两个坦克都在使用时，用过的水箱水样的水质有不同程度的恶化。总的来说,使用双罐运行SWSS将降低一个储罐中水的更换率，使用所提供的SWSS服务的水龙头的消费者可能具有更高的微生物风险。
