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水是如何變質(zhì)的？
[ 2007-10-19 11:22 ]
專題推薦：詞解十七大
在過去沒有自來水的時候，中國人需要去河邊挑水或是用水泵抽取地下水來飲用，這兩種方式都不方便，所以家中常備一個大缸，用來儲水。而近年來，水污染越來越嚴(yán)重，偶爾會出現(xiàn)斷水現(xiàn)象，于是儲水變得不可避免，但是如果方法不當(dāng)，儲存的水很容易變質(zhì)。
Many people store water for emergencies. This is especially true in rural areas where drinking water comes from private wells. These wells are useless unless there is power to run the pump. If you are trying to store water safely, today's question is a great one!
It turns out that there are two ways for water to go bad. You can easily demonstrate the first way by filling a bucket with tap water and leaving it on the back porch for several days. After about a week, you will find that the water in the bucket contains mosquito larvae, algae and various other life forms, none of which you would want to drink. From this experiment, you can easily decide that storing water in an open container is a bad idea unless you have a plan to purify it when you need to drink it. Storing water in a closed container works no better if the water that you place in the container is contaminated in some way with bacteria or algae. You need to put pure water in a clean container and then process it in some way to eliminate bacterial contamination. You can process the water with heat just like you do when canning, or use a chemical like chlorine or iodine.
The second way for water to become unfit for drinking is for something to leak out of the container into the water. As an extreme example, imagine what would happen if you were to store water in a lead container. Lead would leak into the water and make it poisonous. The container you use needs to be made from a special material, called food grade, in order to avoid leaking problems. Glass, stainless steel and some plastics are food grade.
One easy way to store water is to buy purified drinking water in gallon plastic jugs at the grocery store. This water is inexpensive, free of bacterial contamination and is sealed in a food-grade container.
larvae：（昆蟲）幼蟲
algae：藻類
chlorine：氯
iodine：碘, 碘酒
food grade：食品標(biāo)準(zhǔn)
gallon：加侖
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