If your water heater is leaking gas or has a gas combustion issue, you’ll likely smell sulfur or what some describe as “rotten eggs.” However, it’s important to note that natural gas is odorless. To make detecting leaks easier, gas companies add mercaptan, a chemical that gives it that highly recognizable sulfur-like smell. Once you smell the rotten egg smell, shut off the gas to the water heater immediately and leave your house. Call your gas company right away to check for leaks and water heater experts to fix or replace the system.