Sometimes we have to add or get off words when we translate because of the difference of the way to say in each language.
For us, it sounds "incomplete" saying only 浴びる because we distinguish 水を浴びる、シャワーを浴びる、etc so we have to translate "to shower --> シャワーを浴びる", and in the case of your example, you can also say 猫は(someone)に水をかけられた if you want to use the passive voice.
Other examples are:
I like reading --> 私は 本を(or other object)読むことが好きです or 私は読書が好きです。
We ate in the restaurant. --> We need the object, what we ate or I would say 私たちはレストランで食事をしました。
Please remember that sometimes "word by word" translation doesn't sound well nor make sense. I hope this helps you.