Hot only, cold fine: it is the anode rod
Every tank water heater has a sacrificial anode rod, usually magnesium, that corrodes so the steel tank does not. Sulfate-reducing bacteria that are harmless in the cold supply thrive in a warm tank and use the hydrogen the rod gives off to turn sulfate into hydrogen sulfide — the rotten-egg gas. Cold water from the same pipes has no smell because it never met the rod.
The fix is to replace the magnesium rod with an aluminum-zinc rod, which does not feed the reaction; a plumber does it in about half an hour. Running the tank at 140°F for a few hours kills the bacteria but does not stop them returning, and it raises scald risk. A softened supply can make the smell worse because softening increases the water's conductivity; the rod swap fixes that case too.
Both hot and cold, or only one sink: check the drain first
Manatee County Utilities' own odor fact sheet says that in its system "the vast majority of H2S reports by customers are actually caused by odors from drains as opposed to odors in the tap water." Water sitting in the trap under a sink grows bacteria that make hydrogen sulfide; turning on the tap pushes that gas up out of the drain, and the whole bathroom smells within seconds. The county's test: catch the first water from the tap in a cup without letting any go down the drain, walk away from the sink, and smell the cup. No smell in the cup means the drain is the source.
A drain that smells is a cleaning job — the county suggests baking soda and water left in the trap for several hours, or a quarter cup of household bleach for fifteen minutes, then flushed. A drain that smells because its trap has dried out (a guest bath, a seasonal home) just needs water run into it.
The county's 2025 Water Quality Report describes the finished water leaving the plant as odorless; groundwater from the Floridan Aquifer is aerated at the plant specifically to remove the sulfur it carries.
Both hot and cold, every tap, and you are on a well
Outside the county system — the Myakka City side of the county, the edges of Parrish, older properties on private wells — hydrogen sulfide in the raw water is common, and it will be in the cold as well as the hot. That is a whole-house treatment question (aeration or oxidation plus filtration), not an anode rod, and it starts with a water test. The EPA's home drinking-water testing guidance is the place to begin; a plumber who sells you a softener for a sulfur problem has sold you the wrong thing.
When to stop and call a licensed plumber
- The cup test clears the drain and the smell is only in the hot water — that is the anode rod, and it is a half-hour job.
- The heater is over 8 years old: the anode may be entirely consumed, and the visit should include a look at whether the tank is worth the part.
- The smell is in hot and cold water on a private well — you need a water test and a treatment plan, not a heater part.
- Cleaning the trap does not clear a drain smell after two attempts, or the smell is sewer-like throughout the house — that can be a dry trap in an unused fixture, a failed wax ring or a vent problem.
Rosco Plumbing's service call in Manatee County is $75–$150, applied toward the anode-rod replacement that clears a hot-water-only sulfur smell.
Call (941) 345-2464 or request a free estimate. Residential service in Manatee County; ranges are planning figures, not quotes.
Have Rosco Plumbing contact you about this
Describe what you are seeing and Ross will call or text back with what it sounds like and what the visit costs — no obligation.
What changes in Manatee County
In Manatee County the heater version of this smell shows up most in seasonal homes: a tank that sat warm and unused for the summer in a Perico Bay Club, Anna Maria Island or Del Webb home comes back reeking in November. Run the hot taps hard for ten minutes on return; if the smell persists into the next day, it is the rod. The well-water version belongs to the county's eastern edges, where homes are outside the utility system entirely.