The short, stinky answer is hydrogen sulfide gas. It’s a molecule that smells like hell’s own soufflé—rotten eggs, straight up. And no, it’s not because some prankster dropped a dozen eggs into your water heater.
Here’s the science: sulfate-reducing bacteria—tiny, invisible, lazy little microbes—live in your water supply. They love munching on sulfate minerals and turning them into that stinky gas. These bacteria are basically the teenagers of the microbial world: they eat junk, produce stink, and don’t clean up after themselves.
Why It’s Worse When the Water’s Hot
Now, you might notice that cold water from the same tap smells fine. Aromatic, even. But crank up the heat, and BAM—egg-pocalypse. Why? Because heat is like a cheerleader for hydrogen sulfide gas.
Cold water holds that gas dissolved, like bubbles trapped in a soda bottle. But hot water kicks it out—the gas escapes into the air, straight up your nostrils. Think of it like this: cold water is a chill library, hot water is a mosh pit where the stink molecules break free and party in your nose.
Also, your water heater can be a bacteria spa. If it’s set too low (below 140°F or 60°C), those sulfate-loving microbes set up a hot tub and multiply. Warm water + low flow = rotten egg paradise. You’re basically showering in a microbial jacuzzi.
Tankless Water Heater Smells Like Rotten Eggs: Quick Fixes | Smart
