A sulfur smell in well water often indicates bacteria growing in the water. Owners should stop using the water until the problem is corrected, as bacteria is potentially harmful. A musty, earthy or fishy odor sometimes indicates contamination from surface drainage. Solvent-like odors are rare, but sometimes indicate leaking fuel tanks, agricultural contamination or industrial discharges leaking into the well.
If hydrogen sulfide is produced by bacteria in the well, chlorinating the water and then pumping until the chlorine smell disappears is one method of eliminating the odor. If it returns, owners should take steps to determine the source of the contamination. If the wellhead has insufficient protection, surface water runs into the casing and contaminates the water, leading to more odors.
In some cases, well water smells due to sources outside the well. An odor noticed at the sink that disappears when the glass is a few steps away likely indicates a drain issue and not a well problem. If the odor only affects the hot water, the problem could be with the sacrificial rod inside the water heater. Sometimes dissolved minerals in the water react with the plumbing inside the house to cause odors. Odors affecting only one fixture could be a chemical reaction between minerals in the water and the metals in the fixture.