If your water heater smells like gas, you should have it checked out by a professional right away. Gas companies add a chemical to natural gas that makes it smell like rotten eggs. It’s an unmistakable smell and if you notice the smell coming from your water heater, immediately shut off the gas valve and contact your natural gas company. This is one of those problems that requires a professional to solve. Your water heater may also smell like gas when bacteria multiply inside your water heater after turning it off for some time or running it at low temperatures.