2,047. When We Count Days

Hilchos Issurei Biah 4:3

Impurity depends on the days when the woman immerses in a mikvah after these specified number of days. If a niddah, zavah or a woman who has given birth didn’t immerse, then one would be liable for kareis for having relations with her even years later. This is because the Torah made the matter dependent on both days and immersion, as per Leviticus 15:18, “They shall immerse themselves....” This teaches a general rule that any impure person remains in a state of impurity until he immerses.

Hilchos Issurei Biah 4:4

The prohibitions against relations with a niddah, zavah and a woman who has given birth don’t apply to non-Jewish women. The Sages ruled that when it comes to matters of ritual purity and impurity, all non-Jews – both male and female – have rules like a zav at all times regardless of whether or not they experienced such discharges.