在过去没有自来水的时候，中国人需要去河边挑水或是用水泵抽取地下水来饮用，这两种方式都不方便，所以家中常备一个大缸，用来储水。而近年来，水污染越来越严重，偶尔会出现断水现象，于是储水变得不可避免，但是如果方法不当，储存的水很容易变质。

    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：（昆虫）幼虫

    algae：藻类

    chlorine：氯

    iodine：碘, 碘酒

    food grade：食品标准

    gallon：加仑