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Why Does My Water Smell Like Rotten Eggs?

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Why Does My Water Smell Like Rotten Eggs?

If your home's water smells of rotten eggs, or something similarly offensive to the nostrils, it is likely that it contains a compound known as Hydrogen Sulfide (H2S).

What is it?

Hydrogen Sulfide is a gas common to many water sources for many different reasons. It is a harmless by-product of certain types of bacterial reactions. However, it is also a major component of sewage (if this is the origin of your H2S, it is a more serious issue).

How concerned should I be about its presence in my water?

As mentioned above, the origin of the H2S is an important factor to consider when determining the level of danger of the problem. Hydrogen Sulfide alone is only dangerous to humans at high concentrations. Luckily, we can detect its presence at extremely low concentrations (concentrations 400 times lower than a harmful concentration). The odor is so strong that this doesn't seem like such a "lucky" thing at first glance, but if the Hydrogen Sulfide was there merely as a component of sewage in your water you'd be grateful you had such a clear signal.

At the low concentrations that H2S is typically present at, though it is not directly detrimental to your health, it still has a few negative effects. The most obvious effect of its presence is the characteristic "rotten egg" smell of water containing it. Less obvious is that water containing H2S can corrode certain common metals like iron, steel, copper, and brass. Dishwashers operating using water contaminated with Sulfur will, over time, blacken silverware and discolor copper and brass utensils. Clothes run through your washer aren't necessarily safe either; The combination of bleach with Sulfur water is known to reduce the effectiveness of detergents.

How Does H2S Get in the Water Supply?

Hydrogen Sulfide can find its way into your water in a number of ways. It can simply occur naturally in the groundwater. The likelihood of this scenario is highly dependant on location. Certain parts of the country have high Sulfur levels in the groundwater, but levels can vary greatly even acre to acre.

It can also be a by-product of reaction undertaken by so-called sulfur-reducing bacteria present in the well, groundwater, or water distribution system. These bacteria are non-disease producing bacteria.

As previously mentioned, H2S is a large component of sewage. Sewage can find its way into your water through poorly constructed wells or shallow wells built too close to sewer lines or septic tanks. If this scenario is a possibility, it is recommended that the water be tested for Coliform bacteria and Nitrates as the presence of either of these is a health risk, and not merely the aesthetic odor problem that H2S is.

H2S can also be produced "in house" by your water heater or water softener. This is done in two ways:

  1. By creating a warm and therefore hospitable environment for sulfate-reducing bacteria.
  2. As the result of a reaction between sulfates present in the water and the water heater's anode. The anode of a water heater (usually made of Magnesium) is installed in most water heaters to prevent corrosion of the tank and extend its service life.

How Do I Determine the Source of the Hydrogen Sulfide?

To determine where the Sulfur is coming from, and thus how you will remedy the situation, follow these four troubleshooting steps:

  1. You only smell Sulfur from hot water.
    • The problem likely lies with the hot water heater
  2. You smell Sulfur in both hot & cold water, but only from water treated by a water softener.
    • No surprise here, the water softener is the culprit.
  3. The smell is strong at first from both the hot and cold water faucets, but dissipates as the water is ran longer.
    • Because the smell dissipates, the culprit is likely sulfur-reducing bacteria present in the well or water distribution system.
  4. The smell is strong from both hot and cold water faucets and does not dissipate over time.
    • This is likely due to the natural presence of H2S in the groundwater.

Remedies for Each Type of Issue


Elimination Options:

Water Heater:

To start, unless you are very familiar with the operation and maintenance of a hot water heater, we recommend having a qualified professional perform the work! That said, the fix for a water heater issue is to replace the water heater's anode with one of a different material. Many anodes are composed of Magnesium, which reacts with Sulfates in the water to create H2S. Replacing the anode with one made of a less reactive metal, such as Aluminum, will fix the issue.

Water Softener:

If a water softener issue is the diagnosis you will need to contact the manufacturer of your water softener to determine the correct steps to remedy the issue.

Presence of Sulfur-reducing Bacteria:

The well or water distribution system can be shock chlorinated by a qualified professional to kill sulfate-reducing bacteria.

H2S in Groundwater:

Unfortunately, the only way to truly eliminate the problem is to re-drill the well in a location containing H2S-free groundwater. This is easier said than done, as this is typically an expensive and uncertain process. It may be the case that Sulfur is present in all the water on your property. The only way to know for sure is to test the water at a potential well location. Digging a well deeper doesn't fix the problem either as, generally, the deeper the well the higher the mineral Sulfur content.

Treatment Options:

Depending on the origin of the H2S, the methods to completely eliminate the problem may be prohibitively expensive or even impossible. No need to despair though, as there are a few common methods used to treat Sulfur water. The method you should use depends on the concentration of H2S in your water, so you'll need to test the water prior to using any of these methods.

Low H2S concentrations [< 1 part per million (ppm)]:

  • Install an Activated Carbon Filter. These filters are relatively cheap and easy to install. They are rated in microns, a measurement of the pore size of the filter. The lower the micron rating, the tighter the filter. Tighter filters, while they filter more contaminants out from your water (incuding H2S), they also have a much shorter lifespan and need to replaced much more frequently. Lifespans of these filters vary greatly; some last years, others only weeks or days!

Midrange H2S concentrations [up to approximately 6 parts per million (ppm)]:

  • Install an oxidizing filter, such as a "Manganese greensand" filter. Manganese greensand filters are often used to treat iron problems in water. The device consists of Manganese greensand media, which is sand coated with Manganese Dioxide. The Hydrogen Sulfide in the water is changed to tiny particles of sulfur as it passes through the filter. The filter must be periodically regenerated, using Potassium Permanganate, before the capacity of the greensand is exhausted. 

High H2S concentrations [> 6 parts per million (ppm)]:

  • Install an oxidation-filtration system. These systems utilize a chemical feed pump to inject an oxidizing chemical, such as Chlorine or Ozone, into the water-supply line prior to a storage or mixing tank. When sufficient contact time is allowed, the oxidizing chemical changes the Hydrogen Sulfide to Sulfur, which is then removed by a particulate filter, such as a Manganese greensand filter. Excess Chlorine can be removed by activated carbon filtration. If using Ozone as your oxidizing agent, it can be removed via venting or off-gassing.

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