812. Father & Son Mikvah
Halacha restricts visiting a merchatz (bathhouse) with a father or a teacher. Nor should a man accompany his sister's husband or his father-in-law. With regard to avoiding this practice, there are two explanations: one deals with respect (for a teacher or father); the other reason, as explained in the Gemara, is that it may cause hirhurim (inappropriate thoughts).
Although the penchant for public bathing has waned in these days, these halachos would seemingly apply to the many men who frequent the mikvah or swim regularly. But they are generally lenient in all these respects—why?
Some Rishonim (early halachic authorities) explain that this issue applies only to a bathhouse, where the bathtub is an above-ground keli (vessel), but not to a pool or mikvah that is connected to the ground. Many poskim reject this explanation. The Rema (16th century primary commentary on the Shulchan Aruch) says that people are lenient since bathing suits are generally worn for public bathing or swimming. However, this explanation would not apply to a mikvah.
Others make a distinction between a merchatz yavesh (a sauna), patronized for the purpose of "a shvitz" and a bathhouse used for bathing. The halachic issues primarily concern a sauna, they maintain, since at a mikvah, pool or bathhouse, water acts as a cover-up for the state of undress. Additionally, most people sit in a shvitz to socialize or for leisure, while showering, bathing and dipping in the mikvah are time-constrained activities.
Added leniency can also apply to dipping in a mikvah, which is usually in the presence of many others. It would be highly unusual to meet up only with a father, teacher or in-law while there. Many poskim also allow for a father to accompany a small child, since there is less concern for hirhurim. The concern for lack of respect is also mitigated, for the parent (who initiates the visit) is certainly mochel (forgiving [of his honor]).* (Some earlier sources note that a father or teacher should stand on the side, and try to remain inconspicuous when their son or student is around.)
People go to a mikvah for spiritual reasons—for the purpose of purification—and as such it can therefore be argued that there is less need for concern with regard to these restrictions. #812
*It should be noted that a young child should never go unaccompanied to the mikvah for reasons of sakanah (danger).