Rotten-Egg Smell in Well Water
Why well water smells like rotten eggs, how to find the source with two faucets, and what each fix costs.
Start with the hot and cold taps
The smell is hydrogen sulfide gas, which Florida DOH says can occur in wells anywhere in that state. Its odor and staining fact sheet gives a simple test: run the hot and the cold tap separately and note where the smell is.
What the pattern tells you
- Hot water only: the water heater is the likely source; Florida DOH notes chemical reactions inside heaters can produce the smell.
- Only water that passes through the softener: sulfur bacteria living in the softener.
- Strong at first, fading as the water runs, or changing over time: sulfur bacteria in the well or plumbing.
- Strong and steady from hot and cold taps: hydrogen sulfide in the groundwater itself.
Is it dangerous?
Florida DOH notes that sulfur bacteria are not harmful and that the smell usually says nothing about whether the water is safe. It does not replace a bacteria test: test for total coliform and E. coli, which EPA recommends every year for a private well.
Fixes, from cheapest
A water-heater anode swap or a softener cleaning handles the first two cases. Bacteria in the well call for shock chlorination by a licensed pro, then a retest. Hydrogen sulfide in the groundwater needs treatment: an air-injection or catalytic carbon filter for moderate levels, or a peroxide or chlorine feed for strong odor. HomeGuide puts installed hydrogen sulfide treatment at $800 to $3,500 (cited as text). See the cost guide and the iron and sulfur guide.
Sources
Florida DOH, Well water facts: odor and staining; EPA, Protect your home's water; EPA, Secondary Drinking Water Standards; HomeGuide, Well Water Filtration System Cost (Apr 24, 2026, cited as text).
Prices are published US ranges from the sources listed on each page; anything we calculated ourselves is labeled as an estimate. Get at least three written, itemized local quotes. Run the estimator to build your own range.