In most cases, the rotten egg smell does not relate to the sanitary quality of the water. However, in rare instances the gas may result from sewage or other pollution. It is a good idea to have the well tested for the standard sanitary tests of coliform bacteria and nitrate. Sulfur bacteria are not harmful, but hydrogen sulfide gas in the air can be hazardous at high levels. It is important to take steps to remove the gas from the water, or vent the gas to the atmosphere so that it will not collect in low-lying spaces, such as well pits, basements, or enclosed spaces, such as well houses. Only qualified people who have received special training and use proper safety procedures should enter a well pit or other enclosed space where hydrogen sulfide gas may be present.