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Water problem

Sulfur smell

Hydrogen sulfide gas, which smells of rotten eggs. Where the smell appears tells you where the problem is, and that distinction saves most people the cost of a treatment system.

Laboratory hydrogen sulfide test, after isolating hot from cold
Start with the water

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Tell us what you notice at the tap. We will help you sort out the next useful step.

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What you might notice

  • A rotten egg smell at one or more taps
  • The smell is stronger on hot water
  • It is noticeable on first draw then fades

The two minute test that often ends the problem

Run the cold tap on its own for a minute and smell the water. Then run the hot tap on its own and smell that. Do it in that order and pay attention to the difference.

If only the hot water smells, the supply is very likely fine. What is happening is a reaction inside the water heater, between its sacrificial 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. It costs a small fraction of a whole-house treatment system, and it is the reason we always ask people to run this test before booking anything.

When the smell is in the supply

If both hot and cold smell, hydrogen sulfide is dissolved in the water and treatment is warranted. A laboratory test establishes the concentration, and the concentration decides the method.

At low levels a catalytic carbon filter is often enough and needs neither drain nor power. In the middle range, air injection with a filtration stage handles it and backwashes automatically. At the high end, or where iron bacteria are also present, continuous chlorination followed by a contact tank and filtration is the reliable approach.

Hydrogen sulfide is corrosive to copper and tarnishes silver, so where it is genuinely in the supply there is a plumbing argument for treating it as well as a comfort one.

Two things that are easy to confuse with it

A smell at one sink only, stronger when the tap runs slowly, is usually bacteria in the drain rather than anything in the water. Fill a clean glass, carry it to another room, and smell it there. If it smells fine away from the sink, clean the drain and the problem is solved.

Sulfate is not hydrogen sulfide. It is a dissolved salt with no smell at all, and at high concentrations it has a laxative effect. It needs reverse osmosis rather than oxidation, so a test that reports both avoids treating the wrong one.

A smell that appears only after heavy rain, or only seasonally, is worth mentioning, because it can indicate surface water reaching the well.

How to confirm it

Run the cold tap alone, then the hot tap alone. If only the hot water smells, the likely cause is a reaction between the water heater's magnesium anode rod and sulfate-reducing bacteria in the tank, not the supply. If both smell, the gas is in the water and a laboratory test should confirm the concentration.

The test that settles this is laboratory hydrogen sulfide test, after isolating hot from cold. We include what we can measure on site in a free water test, and we will tell you plainly when a certified laboratory is the right next step rather than anything we can do at your kitchen tap.

When not to treat it

When the smell is on hot water only, replacing or removing the anode rod and disinfecting the tank normally resolves it for a fraction of the cost of a whole-house system. A single smelly drain, rather than the water itself, is also a common cause and needs cleaning rather than filtration.

Treatment options that actually apply

These are the equipment types that address this problem. Each page states what the equipment does not do, so you can rule it out quickly if your situation does not match.

What none of these will do

  • 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.

Getting it installed

Once a test has confirmed the problem and narrowed the equipment, the practical questions are access, space, and whether anyone's permission is needed. Those are covered on the installation pages, along with what a visit involves and how long it takes.

Other water problems

Sources

Next step

Confirm the problem before you spend anything.

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