Why Does My Well Water Smell Like Rotten Eggs?

Find the source first

1. Run the cold tap. If cold water smells too, the gas is in the well water itself.
2. Run the hot tap. If only hot water smells, the cause is usually the water heater, not the well.
3. Check after time away. A smell that is strongest after the water has sat, such as first thing in the morning or after a holiday, often points to bacteria in the well or plumbing.

If only the hot water smells

Most water heaters have a magnesium anode rod that protects the tank from corrosion. In some well water, it reacts with sulphate and bacteria to produce hydrogen sulphide. Replacing it with an aluminium-zinc anode, or a powered anode, usually solves the problem. Do not simply remove the anode; the tank will corrode much faster without it.

If the cold water smells too

The gas is in the groundwater, often produced by sulphur-reducing bacteria in the well or the aquifer. Options depend on how strong it is:

• Light smell: an activated carbon filter can be enough
• Moderate to strong smell: an air-injection or oxidizing filter, often combined with iron removal
• Bacterial source: shock chlorination of the well, sometimes followed by ongoing treatment

Iron and sulphur often show up together in this area, which is why one properly chosen filter can fix both the smell and the orange staining.

Is it safe?

At the levels usually found in household water, hydrogen sulphide is mostly a taste and odour problem rather than a health risk. But it can corrode plumbing and fixtures, and the smell itself makes the water unpleasant to use. Because a smell can also come from bacteria, it is worth having the well tested for bacteria as well. Public Health Ontario tests private well water for bacteria free of charge.