Read other letters about this article
The phrase "water baptism" is redundant; no such term exists in popular or theological discourse.
I suspect Mike Madden meant "full-immersion baptism," in which the person being bapized is fully immersed in water (as opposed to the person having water sprinkled on them). Though not synonymous with "full-immersion," I suspect that the phrase "believers' baptism" probably could have applied as well, since I strongly suspect New Life does not practice the baptism of infants.
Additionally, it would have been more accurate to write that the prayer session was going to double for a "service of baptisms for new members" (instead of "a water baptism for new members") so as not to imply that all members were being baptized, in one way or another (but by definition with water), en masse.