Addition of hydrogen atoms

Hi,
I would like to know if anyone knows exactly how Accelrys DS Visualizer 1.7 adds hydrogen atoms to water molecules that are part of an x-ray crystal structure of oligonucleotides. Reason being that it appears to not add them intelligently rendering otherwise useful (stabilizing) water molecules, useless. Is it a random process or based on the hybridization at the oxygen atoms?
Thank you,
Petrina