A rotten egg smell in hot water often indicates hydrogen sulfide gas, which is produced by bacteria in the water heater tank. These bacteria thrive in environments with low oxygen levels, such as the sediment buildup at the bottom of the tank, and produce hydrogen sulfide as a byproduct. The gas is released when the hot water tap is opened, creating a distinctive smell. You should try flushing and cleaning the water heater tank to remove the sediment buildup while disinfecting the tank using hydrogen peroxide or chlorine bleach. This may eliminate the bacteria and reduce the odor. If the problem persists, it may indicate a more severe issue with the water supply or the water heater. In that case, contact Rooter Solutions for further assessment and treatment.