John baptised in the river Jordan, we're told in Matthew's gospel chapter 3:6. This is not according to the mikveh law — John's baptism is in running water, not the still water of mikveh. John's baptism was as a sign of repentance.
Likewise, the gentiles were baptised (Acts 10:47ff) and the Philipian gaoler was baptised, both in cases where the proper bath for Mikveh would not be available.
Ez 36:24
I will take you from the nations and gather you from all the countries and bring you into your own land. [25] I will sprinkle clean water on you, and you shall be clean from all your uncleannesses, and from all your idols I will cleanse you. [26] And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. [27] And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules. [28] You shall dwell in the land that I gave to your fathers, and you shall be my people, and I will be your God.
Firstly, God has already chosen a people for himself. This passage is written to Israel directly, but can be taken to apply to all the ones God has chosen.
Secondly, God calls his people from whereever they are into their own land — his land
Thirdly, it is God who cleanses by pouring water from above. Water here could be taken as a figure for Spirit, or as literal water.
Fourthly, having been cleansed, God changes his people's hearts, to be ones capable of obedience.
Finally, this results in an obedient people, living in God's land, with God dwelling amongst them.