Mikvah is a Hebrew word used to describe a ritual immersion in Judaism. Not just immersion of any type of water, but immersion in a certain way and in a certain type of water.
The word literally means, “a collection”, generally, a collection of water.
The water must come from a flowing river, stream or spring. It cannot be standing or stagnant. The term for this type of water is “living water”. 
The Lord Jesus used this very phrase in John 7:37-39
“In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)”
You and I as believers on the Lord Jesus Christ are in reality artesian wells, springs of living water, and full of the Holy Spirit being poured out in our generation. We too say; if any man thirst let him come to the Lord Jesus Christ and be saved.  He can be found in the well of our lives as we live out His life in a dry and thirsty land.
“For whosoever shall call upon the name of the Lord shall be saved.”
Romans 10:13