Water dripping from the bottom of a heater typically indicates an internal leak or rain water entering through  the exhaust vent.  If you have this problem follow these steps:

1. Isolate the heater:shutoff cold water supply (also turn off hot water if you have isolator valves)
   
2. Turn the remote off (for unit without remote turn gas valve to off position)
   
3. Drain water from unit using either isolator valves or black plastic drain plugs on bottom of heater.
4.  
5. Contact a Noritz Service Representative.  Please visit http://support.noritz.com/servicereplocator.php
6. to find a local servicer.