I noticed this verse the other night and thought it looked so obviously ridiculously provably untrue that there must be something more to it. Surely even a bible writer must understand that desalination isn't witchcraft?
It seems that the NWT and RNWT butcher the translation though (the New American Standard Bible also looks bad):
NEW WORLD TRANSLATION OF THE HOLY SCRIPTURES (2013 REVISION):
"Neither can salt water produce fresh water."
NEW WORLD TRANSLATION OF THE HOLY SCRIPTURES (1984 EDITION):
"Neither can salt water produce sweet water."
New International Version:
"Neither can a salt spring produce fresh water."
New Living Translation:
"No, and you can't draw fresh water from a salty spring."
English Standard Version:
"Neither can a salt pond yield fresh water."
New American Standard Bible:
"Nor can salt water produce fresh."
King James Bible:
"so can no fountain both yield salt water and fresh."