If domestic sewage and industrial waste water can be prevented from flowing into the river, or can be treated before flowing in, and if refuse can be prevented from being dumped on the river banks or into the river, then the river will clean itself naturally.
如果我們能使家庭汙水、工業廢水不流入河流之中，或是經過處理之後，才准流入；垃圾不能隨便傾倒於河岸或河中，河流的水自然會清潔。