The diagram below illustrates how a simple water filter is constructed and how it functions to produce clean drinking water：
开头：
The following chart provides information about the construction of a water filter and the process of producing clean drinking water by the filter.
第一段：描述一下装置
Two major devices are involved in the water filter, a bucket with a wooden cover and a closed tank with a tap. There are three layers in the bucket among which the charcoal is between the sand and gravel. At the bottom of the bucket is a long pipe linking through the three layers to the closed tank.
第二段： 写
There are two basic steps in the production of drinking water. The process starts from pouring impure water into the bucket, which then is filtered through the sand, charcoal and gravel. Afterwards, the water flows through the pipe and finally into the storage tank where clean drinking water is stored. People could drink the water by simply turning on the tap at the lower part of the tank.
结尾：
Overall, it is clear that clean drinking water could be produced through a** two-step process** with a simple water filter.
Afterwards 后来 然后
bucket 桶 水桶
tank 坦克 水槽
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