必须注意的是要严格控制任何化学净水过程。

Care must be taken to ensure strict control of any chemical disinfection process.

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这些老人共同所拥有的就是远离城市的纯净水源，没有化学物质和毒素。

What they all have in common is pure water sources located far from any city, free from chemicals and toxins.

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重点介绍了目前国内供水行业所采用物理、化学以及生物的方法在水厂净水处理及二次供水过程防除摇蚊污染的研究；

Physical, chemical and biological control methods in the purifying water process and the secondary water supply system in Chinese water supply industry are discussed.

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