Under sink 4-gallon point of use water heater servicing the bathroom handwash/toothbrush sink (no appliances or other fixtures) was removed and examined this morning. Magnesium anode rod (~6 inch long, 1 inch diameter) was completely depleted. Residual water in tank, in summary, did not match the chemical, physical, and biological characteristics of the sink output. The appliance was removed from service, (although it still heated water as usual), and will be replaced rather than serviced.