Well, in Christianity, baptism removes original sin.
Now, check out what I found about the mikvah while browsing the Internet:
"Immersion in the mikvah has offered a gateway to purity ever since the creation of man. The Midrash relates that after being banished from Eden, Adam sat in a river that flowed from the garden. This was an integral part of his teshuvah (repentance) process, of his attempt at return to his original perfection." - http://www.chabadofalabama.com/templates/articlecco_cdo/aid/670504/jewish/Why-Mikvah.htm