Water filter type
Sulfur and hydrogen sulfide treatment
Oxidation and filtration aimed at the rotten egg smell. Which method fits depends on concentration and whether the smell appears on hot water only.
Find out where the smell is coming from first
This is the one problem where a five minute test at home can save you the entire cost of a treatment system, so we always ask people to do it before booking anything.
Run the cold tap on its own and smell the water. Then run the hot tap on its own and smell that. If only the hot water smells, the water supply is very likely fine and the reaction is happening inside the water heater, between its magnesium anode rod and sulfate-reducing bacteria living in the tank.
In that case, replacing the anode rod with an aluminium or zinc alloy type and disinfecting the tank normally resolves it. That is a water heater job, and it costs a small fraction of a whole-house system.
When it is genuinely in the supply
If both hot and cold smell, hydrogen sulfide is dissolved in the water itself and treatment is warranted. A laboratory test establishes the concentration, which determines the method.
At low concentrations a catalytic carbon filter can be enough, and it is the simplest option with no drain or power required.
At higher concentrations oxidation followed by filtration is needed, in the same family of equipment used for iron. Air injection systems handle a wide range and backwash automatically. Continuous chlorination with a contact tank covers the highest concentrations and cases where iron bacteria are also present.
Related but different problems
Sulfate is not the same as hydrogen sulfide. Sulfate is a dissolved salt, it has no smell, and at high levels it has a laxative effect. It needs reverse osmosis, not oxidation.
A smell that appears at one sink only, and is stronger with the tap running slowly, is usually bacteria in the drain rather than anything in the water. Pour a little water into a clean glass, take it to another room, and smell it there. If it smells fine away from the sink, clean the drain.
Hydrogen sulfide is corrosive to copper and can tarnish silver, so where it is present in the supply it is worth treating for the plumbing's sake as well as the smell.
What it reduces, and under which standard
Each row names the NSF/ANSI standard the category is tested under. A standard describes what the test covers. It does not mean every unit on the market carries that certification, so check the specific model against its listing before you buy.
| Contaminant | Standard | Note |
|---|---|---|
| Hydrogen sulfide odour | NSF/ANSI 42 |
What it does not do
Every filter has a boundary. These are the things this one will not fix, listed so you can rule it out quickly if your problem is on the list.
- Smell that appears only on the hot tap, which usually points to the water heater anode rod rather than the supply.
- Sulfate, which is a different compound and needs reverse osmosis.
- Bacteria, hardness, or metals.
When it fits
- A clear rotten egg smell on both hot and cold water
- A well test confirms hydrogen sulfide
- The smell is strong enough to affect drinking and cooking
When it does not fit
- Only the hot water smells, where replacing the anode rod is the cheaper first step
- The smell comes from one drain rather than the water itself
- No test has established the concentration
Space, services, and upkeep
A tank at the main line, roughly 1 foot by 5 feet, with drain access for backwashing types.
A drain connection is required. It needs a power outlet within reach. This is not a rental option, because it fixes to the building and stays there.
Replacement interval. Media replaced every 3 to 8 years depending on method and load.
Problems this is used for
We recommend this equipment against these confirmed problems. Each page explains how to confirm the problem before spending anything, and when treatment is not warranted.
- Sulfur smell. Hydrogen sulfide gas, which smells of rotten eggs.
Common questions
Only my hot water smells. What does that mean?
It usually means the water supply is fine and the reaction is happening inside your water heater, between its magnesium anode rod and sulfate-reducing bacteria living in the tank. Replacing the anode with an aluminium or zinc alloy type and disinfecting the tank normally resolves it. That is a water heater job costing a small fraction of a whole-house treatment system, which is why we always ask people to test hot and cold separately first.
Is hydrogen sulfide dangerous to drink?
At the concentrations normally found in a domestic well it is treated as an aesthetic problem rather than a health one, which is why it falls under secondary standards. It is genuinely unpleasant, it corrodes copper, and it tarnishes silver. High concentrations should be assessed properly rather than assumed harmless, and a laboratory test establishes where you sit.
Will a standard carbon filter fix it?
At low concentrations a catalytic carbon filter can be enough, and it is the simplest option because it needs neither drain nor power. Standard carbon has much less capacity for hydrogen sulfide and exhausts quickly. Above low concentrations the reliable approach is oxidation followed by filtration, which is why the test result decides the method rather than the other way round.
Other filter types to compare
If the notes above rule this out, these are the neighbouring options worth reading before you decide.
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