He is taking [drinking] the waters at Bath. 他在巴斯进行矿泉治疗。

四、表示“洪水”等大量的水时，习惯上要用复数。如：

The flood waters are going down. 洪水渐退。

The dam was not strong enough to hold back the flood waters. 水坝不太坚固，挡不住洪水。

五、表示几条不同河流或海域的水，习惯上要用复数。如：

The waters of the two rivers mingled (together) to form one river. 两条河汇合成一条。

六、在某些固定表达中，习惯上用复数。如：

in smooth water(s) 进展顺利，一帆风顺

pour oil on troubled waters平息风波，作和事佬，调停争端

fish in muddy waters 趁火打劫，混水摸鱼

fish in troubled waters 混水摸鱼