March 22 is World Water Day. It started in 1993. It not only makes us think about the importance of water, but also calls on us to1 and protect water. Today, we're facing terrible water problems. Among them, the wastewater problem is rather 2 , And the subject of World Water Day in 2017 is "wastewater".

What is wastewater? It is used water. Usually, wastewater comes from homes, 3 , hospital and so on. It is produced by different kinds of activities, including washing machines, taking showers and using kitchens. The rain also4 wastewater when it is running down the street during a storm. No matter where it comes from, this kind of water is sure to have5 harmful in it. 

6 must we treat wastewater? Wastewater has a big influence in our lives. It causes both illness for us and pollution for the environment. We must care for our environment and our own7 . 

How can we treat wastewater? Different kinds of wastewater need different ways of treatment. Wastewater8 homes can be reused. Then there will be9 wastewater. Also, factory wastewater has to be cleaned10 it goes back to nature.