Hydrogen sulphide is the form of sulphur responsible for the "rotten egg" odour which people find objectionable. Hydrogen sulphide can be found inherently in water, especially when that water is drawn from certain deep, old aquifers. Other wells may be generating hydrogen sulphide as a byproduct of biofouling bacteria.
A low concentration of hydrogen sulphide can sometimes be controlled through periodic shocking of the well with Wellrific. The installation of an activated carbon filter or a down well injection system works well for treating higher hydrogen sulphide concentrations.