Common Causes
Hydrogen sulfide, sulfides, sulfate reducing bacteria in groundwater. There is no standard but any amount can cause these symptoms. Note: odor at one sink may be caused by bacteria in drain rather than water (disinfect drain to remove odor).
Possible Solutions
Shock chlorination of well (in some cases), oxidizing filter, continuous chlorination and filtration. Activated carbon filtration may be used for less severe cases.