Why does my hot water smell like rotten eggs?

A rotten-egg smell only in hot water can come from reactions inside a water heater or the water supply, particularly where certain bacteria and heater components interact. That is different from the odor of leaking natural gas, which requires immediate caution. Compare hot and cold water at more than one fixture without lingering around a suspected gas smell. If you suspect gas, leave the home and call 911 and Oklahoma Natural Gas at 800-458-4251 from outside. If the odor is clearly limited to hot water, stop using affected water for drinking until the source is assessed and ask about water testing and heater inspection.