I get the same smell if I don't drain my hot water heater, and it sits for a couple of weeks, I cant really drain it because it has a hot rod in place where the drain plug is, so I open up the pressure valve on the water heater and close all other valves and pump air through the city water connections, I make sure the pressure regulator on my air compressor is only at 30 psi, this will force most of the water out of the water heater.
but first drain you water and run a bleach/water solution through your whole water system, facets etc..... let it sit overnight, then drain and rinse, and you will be good to go