You turn on the hot tap in the kitchen and get hit with a smell like a struck match or a spoiled egg. You check the cold tap and it smells fine. That split is the most useful clue you have, and it narrows the search faster than any shopping list.
Start with a simple two-tap check. Run the cold tap for a minute, then the hot tap for a minute, and sniff each one right at the faucet. Repeat in a second bathroom if you have one. If both taps smell, the problem is more likely in the water supply itself, whether that is a private well, a city source, or something on the main line. If only the hot side smells, your water heater becomes the first suspect.
Why the hot side is the usual suspect
Water heaters are a common source of sulfur odor. Many tanks contain an anode rod, a metal rod that slows corrosion inside the tank. Some rods are made of magnesium or aluminum, and under the right conditions, bacteria that live in the tank can produce hydrogen sulfide gas, which is the source of that rotten egg smell. Heat tends to make the odor stronger, which is why it often shows up on the hot side only.
Not every case is the anode, and not every sulfur smell is a bacteria problem. But the hot-only pattern tells you where to look before you pay for anything.
What to check before you call anyone
Work through these in order. Most of them cost nothing.
First, confirm the smell is coming from the water and not a drain. Run the hot tap and sniff, then check a sink that rarely runs. Drain odors often fade after a few minutes of running water, while a water heater smell tends to stay put.
Second, look at the age and setup of the water heater. If the tank is several years old and nobody has ever checked the anode rod, that is worth a call to a plumber. Do not try to pull the rod yourself unless you know your tank and have the right tools, since a stuck rod and a disturbed tank can turn one problem into two.
Third, if you have a private well, the sulfur may come from the well itself. Well water can carry dissolved sulfur, and the cold side may smell too. The two-tap check still helps, but the fix looks different and often starts with a full water test rather than a plumbing repair.
Fourth, know the difference between sulfur and gas. Natural gas utilities add an odorant so leaks are detectable. If the smell is strong, comes with a hissing sound, or seems to come from near a gas appliance, leave the area and call your gas utility or emergency number from outside. That is a separate problem from the tap, and it does not wait for a repair appointment.
Where a filter fits, and where it does not
A filter can help with some sulfur problems, but the cause decides the fix. Depending on what you find, the answer may be an anode change, a water heater flush, or a disinfection step, with a filter considered only after that. Buying a filter before you know the source often leaves you with the same smell and a new cartridge bill.
If you want a second opinion on the water itself, Jones Air & Water offer free in-home water tests, which can confirm whether the smell is tied to the water or to the hot line. Ask for the results in writing so you can compare them with what your plumber finds.
The bigger water story is not this smell
Circle of Blue's reporting by Abigail Mihaly, in its look at what comes next for federal water money, describes communities "facing a federal water infrastructure funding cliff" as a bipartisan cash infusion expires. Money decisions like that shape how cities pay for pipe repairs over time, but they do not change what comes out of your hot tap this week. Your home check is still the fastest way to get an answer.
Run the two-tap test tonight, write down what you smell and where, and bring that note to whoever comes to look at the heater. A clear description saves time, and it keeps the first fix focused on the real cause.