• Hydrogen sulphide gas produces an offensive "rotten egg" or "swampy "  odour and taste in the water. In some cases, the odour may be noticeable only when the water is first turned on or when hot water is run. Heat forces the gas into the air, which may cause the odour to be especially offensive in a shower.

    Hydrogen sulphide, or H2S, is a gas common to many groundwater systems across Canada. Hydrogen Sulphide is naturally occurring in groundwater. It is released into groundwater from the rock formations it passes through or occurs as a by-product from sulphur-reducing bacteria. Hydrogen sulphide is most often present in high iron-bearing water, and low or acidic pH waters.

    Hydrogen sulphide is colourless, and readily escapes water giving off a distinct rotten egg or swampy odour. Hydrogen sulphide gas in drinking water is mostly a nuisance and it does not pose a health risk despite the noxiously bad odours and taste they cause in your water. The odours are very strong and can be detected at very low levels as 0.25mg/L. Because hydrogen sulphide readily escapes from water, the best way to sample for it is directly at the source.

    Occasionally, a hot water heater is a source of hydrogen sulfide odour. The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulphide.

    High levels of hydrogen sulphide can be very corrosive and can damage steel, copper plumbing and brass. It can tarnish silverware and discolour copper and brass utensils. Hydrogen sulphide can also cause yellow or black stains on kitchen and bathroom fixtures. Coffee, tea and other beverages made with water containing hydrogen sulphide may be discoloured and the appearance and taste of cooked foods can be affected. High concentrations of dissolved hydrogen sulfide also can foul the resin bed of water softeners. Water softeners provide a convenient environment for these bacteria to grow. A "salt-loving" bacteria, that uses sulfates as an energy source, may produce a black slime inside water softeners.

    When a hydrogen sulphide odour occurs in treated water (softened or filtered) and no hydrogen sulphide is detected in the non-treated water, it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Blackening of water or dark slime coating the inside of toilet tanks may indicate a sulfur-oxidizing bacteria problem. Sulfur-oxidizing bacteria are less common than sulphur-reducing bacteria.