This method was later copied by the apostles. The Ethiopian eunuch obviously had water in his chariot for such a long trip, but he clearly knew that he had to be immersed. Nowhere in the scriptures was sprinkling, pouring, or any other method used, other than full immersion. The word baptism is a Greek word which means to dip, or immerse. It has no other meaning.
Religious encyclopedias are in agreement that the earliest form of baptism was immersion in water.
The method of baptism in the early church according to the Bible was full one full immersion in the name of the Lord Jesus Christ. Anything else is non-biblical.