The Mishnah (Beitzah 36) states that swimming on Shabbat is prohibited due to a Shevut (a Rabbinic decree). However, if the pool is in a private home and has a rim (Safa)—meaning it is not like a flowing spring but is fenced and contained—and the individual requires it for health reasons, such as aquatic physical therapy, one may be lenient, provided it is done in private (B’tzina).

It must be done specifically in private because the common practice is to prohibit it entirely, not based on the strict law alone, but to ensure that the sanctity of Shabbat is not treated with disrespect (Zilzul Shabbat).