行业专家估计，几乎所有此类热水器的水中都含有因重复加热而导致水中的硝酸盐产生的大量亚硝酸盐。
Industry officials estimated that almost all the water produced by such heaters contains high levels of nitrite - produced from nitrate in water that is repeatedly heated.
如果在加热时冒烟、颜色变为深棕色，或者有恶臭味，重复使用则不安全。
If it smokes upon heating, turns deep brown, or has a foul odor, it is not safe to reuse.
这类材料由具有加热软化、冷却硬化甚至可重复循环能力的聚合物组成。
This class of materials consists of polymers which always remain capable of being softened by heat and of hardening on cooling, even after repeated cycling.
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