IMPORTANT!!! If you notice the smell inside or outside your home, as a safety measure you should first call your gas company to investigate.
To track down the source of a rotten egg smell that you feel is water related, first check your drainpipes.
If you have a shower, tub, floor drain or sink that gets minimal use, the odor could be caused by sewer gas filtering into your home through an empty plumbing trap. Sewer gas contains methane, which has a distinctive sulfur smell.
The drains from your fixtures all connect to the main sewer pipe that exits your home. If you haven’t used a particular shower or tub in the past few weeks, the water in the trap may have evaporated and is now allowing sewer gas to seep in.
To find out if a dry trap is the culprit, follow your nose to the room containing the little-used fixture—the smell will likely be much stronger there. If the dry trap is to blame, the fix is simple: Just turn on the faucet a few seconds and let the water run. The water will fill the trap inside the drain and effectively block sewer gases.
If the smell is strongest in your basement, the floor drain trap may have dried out. Pour a pitcher of water down the floor drain to refill the trap. If the smell dissipates, you’ve solved the problem.
If it only smells when you run the hot water
If you only smell the rotten eggs when you run the hot water, the problem is likely with your water heater. If the anode rod in the water heater goes bad, it can introduce a sulfur smell into the hot water supply inside your home. The odor can be mild at first, and then become overwhelming over a period of time.
Chemicals in the water can react to the anode, resulting is a sulfur smell indoors. If you have a water softener, you’re at an increased risk of the anode having a chemical reaction to other elements in the water.
Try a sink test using first straight cold and then hot water. If you notice the odor only when you run the hot water, the anode rod is the likely culprit. A licensed plumber can replace the existing anode and should not require replacing the entire unit.
If you have done all the previous tests steps
If you’ve exhausted the previous steps in trying to determine the source of the sulfur smell in the house, it’s time to call a plumber to check your sewer service lines. A broken drainpipe can allow sewer gasses leak out and invade your home. In the case of a broken line, the smell could be even stronger outdoors than indoors, if the break is located in a part of the pipe that’s buried in the yard.