The Didache relates that a person should be immersed in living (moving) water or standing water. If that isn't possible, then pouring water thrice on the head is an acceptable alternative. For the early church, pouring was not the normative.
Alpha and Omega Ministries is a Christian apologetics organization based in Phoenix, Arizona. James White, director, is a professor, having taught Greek, Systematic Theology, and various topics in the field of apologetics for numerous schools.