Resident complains that hot water in apartment has a bad odor. What is most likely the problem and how do you fix it?

Smelly hot water is usually caused by the anode rod interacting with the water. It sounds like some minerals have leeched into your system and have interacted with the magnesium anode rod in your water heater creating hydrogen sulfate gas. The rod is located under the large looking nut on top of your heater. First try flushing out your heater. Attach a hose on the boiler drain located at the bottom of the heater. With the pressure left on open the hose bib and let the water run until it's clear. If the problem persists, change the anode rod to aluminum. Good luck, Tom