说明节约用水的重要性；
提出节约用水的具体方法；
发出号召。
One possible version:
How to save water
We can never over emphasize the importance of saving water. But we are now wasting a large amount of water in our daily life.
It’s estimated that about 70％of the water used in a family can every day can be saved if we follow the tips below. First, use recycled water. For example, you can use the water to wash rice first, and then use it to wash vegetables, and finally the water can be used to wash the toilet. Second, when you are taking a bath, turn down the tap a little bit. Remember to shut it off in time if you are not using it. Third, when you are washing dishes, use some paper to clean them first, and then use the water to wash them, which will save much water.
Only when everyone takes an active part can we really help save our limited water source.
试题分析：本文是材料和图表结合的作文，通过认真读题，我们明白了写作要求和目的。本文要求说明节约用水的重要性；提出节约用水的具体方法；发出号召。应该用第二人称，时态以一般现在时为主。写作前最好先根据给出的提纲，写出有关的短语和固定表达备用。最后串联起来。
【亮点说明】 本文做到了包含所有内容层次清楚，语句通顺，标点符号运用正确。在100词左右的篇幅中，恰当地运用了一些短语和句式，如It’s estimated that…和when引导的'状语从句，which引导的定语从句，尤其是最后，only加状语句子倒装都是较高级的表达。还有recycled ，in time等比较高级的词汇都可圈可点。