Cleaning up the water supply is their top priority.
清洗供水系统是他们的首要任务。
《柯林斯英汉双解大词典》
2
A few years ago, we started this kind of "favor war" where one of us would do something kind for the other, such as cleaning up the driveway or building a shed, and next time the other would try to top it with another favor.