Get Informed | Dissolved Gasses

What are Dissolved Gasses? 

There are a number of dissolved gases in water that may be a problem or concern. In general, these gases do not have a specific drinking water standard. In this section we will discuss four gases: carbon dioxide, hydrogen sulfide, methane, and radon.

Carbon Dioxide (City Water, Well Water, and Spring Water) - Levels of carbon dioxide may be high within a water source for a number of reasons which include, a change in temperature that causes the dissolved gas to just start coming out of solution or bacterial regrowth in the distribution system increasing the level of carbon dioxide in the water. Note: The presence of carbon dioxide in the water does not mean the water has bacteria. As the carbon dioxide comes out of solution, the pH of the water will increase. Typically, the water may appear "milky" and if you allow a glass of water to set undisturbed on the counter, the water clears in a few minutes from the bottom up. If it takes over 2 minutes for the gas and water to separate and if this is associated with an increase in the pH of the water the gas may be carbon dioxide.

Hydrogen Sulfide (Well Water and Spring Water; rare in City Water) - A hydrogen sulfide or rotten-egg smell can be associated with the presence of hydrogen sulfide gas. This gas may be present because the water is coming from a deep water-bearing zone, or a portion of a distribution system that is very low in or has no oxygen, which may suggest that a disease-causing agent or nuisance bacteria may be present. If this condition is only in the hot water, this could be because of the type of anode rod in the water heater.

Sulfur (Well Water and Spring Water) - The water has an odor like the smell from mercaptans (sulfur compounds) that have been added to natural gas or propane. We have worked on a number of projects where a leaky propane or natural gas line has caused local groundwater sources to have a sulfur odor.

Methane (Well Water and Spring Water) - this gas is typically associated with wetlands, bogs, landfills, coal-producing formations, natural saline seeps, sources of natural gas like the Marcellus Shale, oil fields, some shallower glacial deposits, and natural gas storage areas. Methane is a colorless, odorless gas that is lighter than air. Natural gas is mostly methane (70 – 90 % CH₄), carbon dioxide (0 to 8 % CO₂), plus traces of other gases such as ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and hydrogen sulfide (H₂S) as well as small amounts of helium. Methane is not considered toxic, but it is an asphyxiant at a concentration of over 50 percent in air (it displaces oxygen). Therefore, the primary risks for methane would be asphyxiation in a confined or poorly-vented area; it is also a potential explosion hazard. As a safety measure, the natural gas industry adds mercaptans to the produced methane gas that enters the pipeline and your home. The mercaptans produce a very pungent odor so that gas leaks will be noticed, but unprocessed methane gas tends to have NO ODOR. It is critical to note that some unprocessed methane gas may contain long chain hydrocarbon molecules that may have an odor. You may suspect the presence of methane gas in your water if you hear a “gurgling noise”, sputtering at the tap, the water has a lot of gas bubbles, is effervescent or fizzy. Typically, the gas comes out of solution very quickly.

Radon Gas (Well Water) - Radon is a gas produced by the radioactive decay of the element radium. Radioactive decay is a natural, spontaneous process in which an atom of one element decays or breaks down to form another element by losing atomic particles (protons, neutrons, or electrons). Radon gas in water has no odor or color and does not produce any gas bubbles or fizz; it is detectable only through its radioactivity.

How Do Dissolved Gases become a problem?

In most cases, these gases create a nuisance, but in the case of Radon or Hydrogen Sulfide, there may be a health-related issue, Methane is flammable and, in large quantities, can lead to asphyxiation. High levels of carbon dioxide in the water can cause aesthetic issues and reduce the pH of the water. Hydrogen sulfide may be associated with corrosion of fixtures and is flammable and poisonous. Usually it is not a health risk at concentrations present in household water, except in very high concentrations. While such concentrations are rare, hydrogen sulfide's presence in drinking water, when released in confined areas, has been known to cause nausea, illness and, in extreme cases, death.

What are the Health Risks for Dissolved Gasses?

Dissolved carbon dioxide makes the water more acidic and corrosive which leads to higher concentrations of metals in the water. Most of the other problems with dissolved gasses are that they don’t stay dissolved in the water but become part of indoor air; showers and washing machines are especially efficient at getting dissolved gasses out of water and into the air. Radon in air is associated with lung cancer. Hydrogen sulfide can irritate the throat tissue so much that the throat swells shut, causing asphyxiation.  Methane and carbon dioxide can also cause asphyxiation but only if present in large enough quantities to displace oxygen. Methane is flammable and can even be an explosion hazard.

What are the Standards for Dissolved Gasses?

Methane - The US Department of the Interior, Office of Surface Mining, suggests that when the level of methane gas in the water is less than 10 mg/L it is safe, but monitoring is required at 10 to 28 mg/L, and immediate action is needed above 28 mg/L. At a level of 28 mg/L, the water is fully saturated with methane and it is likely that any air space in the well is at or approaching the LEL. The air and out-gassing methane, not the water, is now flammable.

Radon - The United States Environmental Protection Agency is reportedly prepared to set a maximum contaminant Level of 300 to 4,000 picocuries per liter (pCi/L) standard for radon in drinking water. "At high levels (i.e. among mine workers) radon is a known human carcinogen. There is, however, epidemiological evidence that low levels present no increased cancer risk" (Journal of the National Cancer Institute, Dec. 1994). Note that while radon in air is associated with lung cancer, radon in water is not associated with any kind of cancer.

There are Secondary Drinking Water Standards related to the presence of Odor (Threshold Odor Number) and Color.

Get Tested | Dissolved Gasses

Testing for dissolved gases can be difficult and, in most cases, specialized sampling equipment and field preservation is required, but you can see, hear, and smell problems that may be associated with a dissolved gas. Your senses will not help you detect radon in water, but if you have a Radon level in your home approaching or over 4 pCi/L, we recommend testing your well water for radon. Note, however, that permissible levels of radon in water are much higher than the standard for radon in air.