One possible version：
Dear Jim,
Nice hearing from you. Let me tell you what we often do on World Water Day. On March 22 ndall the teachers and students of the school take part in different activities.
Lots of students put on short plays. Some plays are funny, and they show us wasting water is bad for humans. Many students take part in the speech competition. They tell us what we should do to save water. Some teachers and students make posters and put them up in the school and neighborhood. In this way, more people know the World Water Day and join us.
All these activities are helpful. More and more people know the importance of water and begin to save it. Maybe you do the same.
Yours,
Liu Hong
参考词汇：take part in, put on short plays, speech competition, make poster, helpful, save, waste