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Hydrogen Sulphide (H2S) is a volatile gas that is found naturally in some well water supplies. It causes a foul odour often described as “rotten eggs”. The intensity of the odour depends on the amount of Hydrogen Sulphide contained in the water.
Some facts about H2S:
At the level found in well waters H2S is not harmful. It is the objectionable odour that prompts most homeowners to seek treatment. Only at excessively high, extremely rare cases is Hydrogen Sulphide considered dangerous In such cases, the smell would be so overpoweringly sickening as to preclude anyone thinking of entering an affected area. Due to its activity as a weak acid, at very high levels H2S can promote slight corrosion It can cause silver to tarnish
H2S gas is trapped in the ground and moves with the water as it is being pumped from the well. Being volatile, it takes the opportunity to escape from the water whenever a tap is turned on and pressure is released. This is the reason why the smell is most noticeable when running the kitchen cold tap, or any point of use fed directly from the pump.
Homes where all points of use are fed directly from the well: i.e. a fully pressurised system, sometimes notice the strongest “bad egg/foul odour” coming from the hot water. If you experience this in your home, be sure to bring this to our attention.
In homes where taps are fed from an attic storage tank, the smell is sometimes only noticed at the direct feed kitchen cold tap. This is because at moderately low levels, H2S will escape from the non-pressurised attic tank, dissipating into the atmosphere. At moderate levels, the smell from the kitchen cold tap will be greater than from the indirect, attic fed taps. At higher concentrations, even homes with attic tanks will experience the H2S smell at all taps, showers, or other water using appliances.
H2S levels vary between wells. Levels can also fluctuate quite dramatically in an individual well. For no apparent reason a very slight odour can suddenly become a very obvious bad smell. H2S can even totally disappear for a period of time.
The only predictable thing about H2S is its un-predictability. This makes anticipating the degree of problem difficult when considering treatment. It is therefore important to take into account the pattern of behaviour in an individual supply before deciding on a particular method of treatment.
Methods of treatment
For very low levels it is possible to use a simple in line carbon filter cartridge system. This is usually fitted only on a drinking water line.
If a carbon cartridge filter system is unable to handle the level of H2s then it is necessary to install a larger in line pressure vessel carbon filter system.
The carbon in this system needs to be replaced once its capacity for holding H2s has been reached. The length of time between refills will vary depending on the amount of water used and the amount of H2S to remove. Ideally an annual change of carbon is ideal.
For seriously high levels it is also necessary to chlorinate the water before the carbon filter. In certain situations levels have been so high that we have chlorinated the water which then goes to a storage tank for venting, before being pumped through the carbon for full removal of H2S. Thankfully the need for this belt and braces approach is pretty rare.
It is not unusual to install the smaller filters to begin with and upgrade to the larger systems on a step by step basis as necessary. The idea being to end up with the least complicated system that solves the problem.
Many waters that contain hydrogen sulphide , also contain iron and/or manganese. In such cases the treatment requirements will be somewhat different and should be discussed in detail with one of our water quality advisor's.
Many waters that contain hydrogen sulphide , also contain iron and/or manganese. In such cases the treatment requirements will be somewhat different and should be discussed in detail with one of our water quality advisor's.