I'm looking for the source of the mitzvah of going to the mikvah after being in niddah. There is a part in vayikra 15 which speak about niddah, but there it says a woman should bring a korban when she is finished being in niddah. What I'm looking for is where the mitzvah of going to the mikvah comes from. Looking at verse 19 and on, I can find a lot of verses teaching that anything or anyone one who comes in contact with a woman being in niddah becomes ‘unclean’, but none of those talk about the woman herself having to bathe in living waters, only about the counting of days after which she is considered to be clean (verse 28).
The only verse I could think of was 15:13 if we take it as a general rule it could be read as: When one (male or female) with a discharge becomes clean of the discharge, one shall count off seven days for ones cleansing, wash ones clothes, and bathe ones body in fresh water; then one shall be clean.
Any other thoughts or sources derived from the verses mentioned in Leviticus 15 which could show us a reason for taking a mikvah?
[P.s. would it be allowed to take a normal bath if there isn’t such a command to be found?]