water pollution source

例句：

1. 1. The source of the pollution is often difficult to trace.
   污染来源往往难以追踪。
2. 2. The source of this problem needs to be identified and addressed.
   这个问题的根源需要被识别并解决。
3. 3. The government has set up a hotline to help people report sources of pollution.
   政府已经设立了热线，帮助人们报告污染源。