First the argus then the water monitor......those are two of the worse monitors for people beginning with monitors. I would take it back to the pet store...just like you did with the argus.

That 'little guy' won't take long to be one of the largest available captive lizards(6'+) if taken care of properly and should be housed in a very large enclosure.

http://www.proexotics.com/care_water.html