This needs to involve Japanese bathing culture. Japan is a country that likes hot springs and bathing very much, so the bathtub is a necessary household item for every family in Japan. Naruto tells a story similar to that of an ancient ninja, so there is no such developed life at all. Many people still like to take a bath in public bathrooms, which can also make them more relaxed and clean their bodies better in the process of taking a bath.
If everyone in the cartoon likes to take a bath at home, then many classic pictures in this cartoon will not appear. Because there are many pictures about bathing in the whole animation, and in the process of bathing, we also find that these characters will exchange some very important information. The author wants to enrich the whole animated character scene in this way, and at this time he will reveal a lot of relevant information about the story process to our audience by taking a bath.
Therefore, the reason why the author draws such a picture is not only to promote the development of the plot, but also to inherit the traditional Japanese bathing culture to a certain extent, which is also an indispensable plot and fragment for the audience.