זָב שֶׁרָאָה קֶרִי, וְנִדָּה שֶׁפָּלְטָה שִׁכְבַת זֶרַע, וְהַמְשַׁמֶּשֶׁת שֶׁרָאֲתָה נִדָּה - צְרִיכִין טְבִילָה. וְרַבִּי יְהוּדָה פּוֹטֵר.
A Zav who saw a seminal emission, a niddah who emitted semen from prior sexual relations and a woman who had marital relations that saw her niddah (period): they are required to immerse in a mikvah. However, Rabbi Yehudah exempts them [from mikvah in-order to study Torah].
Don't fully understand some of the words I don't understand some of the language, or why some of the words aren't in English, but what is says is merely common sense, well to us of the 21st century, but perhaps not to those in ancient times especially if water was scarce.