While checking on the laser this morning I noticed the diode chiller warning light (on the LASER MEDM screen) turn red briefly, then back to green.  I went to the chiller room and hung out for a few minutes, watching the diode chiller, and sure enough it was intermittently flashing a "Low Water Level" warning (not an alarm, just a warning).  I added 500 mL of water and this behavior quit.