Hydrogen Sulfide in Drinking Water

Sulfur bacteria are not harmful, but hydrogen sulfide gas in the air can be hazardous at high levels. It is important to take steps to remove the gas from the water, or vent the gas to the outside so that it does not collect in low-lying spaces—such as well pits, basements or enclosed spaces (for example, well houses).

In most cases, the rotten egg smell does not mean your water quality is bad. However, the gas may be present as a result of sewage or other pollution in rare cases. That's why it's best to also test your well for total coliform bacteria and nitrate. Learn more about testing your well water

When sulfate or other sulfur-containing minerals are broken down, they turn into hydrogen sulfide gas, which can get into your water. This can happen in several different ways:

• It can occur naturally from the decay of vegetation or from some sulfur-containing minerals in the soil and rock. These minerals dissolve in groundwater as it moves through the soil and rock formations.
• It can be produced by certain "sulfur bacteria" in the groundwater, in the well, or in the plumbing.
• It can be produced inside water heaters either by creating an ideal warm environment where sulfur bacteria can live or by chemical reactions between sulfate in the water and the water heater anode. An anode is a metal rod, usually made of magnesium metal, that is installed to reduce corrosion of the water heater tank.
• In rare instances, it can come from pollution.

Hydrogen sulfide gas can be smelled in water at a very low level. Smell the water coming out of the hot and cold water faucets to find out which faucets have the "rotten egg" smell. It will often be more noticeable from the hot water because more of the gas is vaporized. Your sense of smell becomes dull quickly, so the best time to check is after you have been away from your home for a few hours.

• If the smell is only from the hot water faucet, the problem is likely to be in the water heater.
• If the smell is in both the hot and cold faucets, but only from the water treated by a water softener (and not in the untreated water), the problem is likely to be sulfur bacteria in the water softener.
• If the smell is strong when the water in both the hot and cold faucets is first turned on, and it goes away after the water has run for a while, or if the smell comes and goes, the problem is likely to be sulfur bacteria in the well or plumbing.
• If the smell is strong when the water in both the hot and cold faucets is first turned on, and is more or less constant and does not go away, the problem is likely to be hydrogen sulfide in the groundwater.

The amount of hydrogen sulfide in water can be determined by some private laboratories. Search for a certified drinking water lab

If you determine that the problem is the groundwater, you can have a water treatment specialist come out and measure the concentration of the gas directly from your faucet. The water treatment specialist can help determine the best treatment option based on the measurement. Find a water treatment specialist

The source of the gas is important when considering treatment options.

Well, plumbing or water softeners

For sulfur bacteria that are present in the well, plumbing or water softener:

• Disinfect the well and plumbing by flushing with a strong chlorine solution, which is called shock chlorination. Sulfur bacteria can be difficult to remove once established in a well. You may need to scrub the well casing, use special treatment chemicals, and agitate the water to remove the bacteria before disinfection. Find a licensed well contractor
• If the bacteria are in water treatment devices—such as a water softener—contact the manufacturer or the installer to find out how to disinfect the treatment devices.

Groundwater

If hydrogen sulfide gas is in the groundwater, you can install one of these water treatment systems:

Activated carbon filter

This is only effective for low hydrogen sulfide levels, usually less than 1 mg/L (milligram per liter). The gas is trapped by the carbon until the filter is saturated. Since the carbon filter can remove substances in addition to hydrogen sulfide gas, it is difficult to predict how long it will last. Some large carbon filters have been known to last for years, while some small filters may last for only weeks or even days.

Oxidizing filter (for example, "manganese greensand" filter)

This is effective for hydrogen sulfide levels up to about 6 mg/L. 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 gas 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.

Oxidation-filtration system

This is effective for hydrogen sulfide levels up to and exceeding 6 mg/L. These systems utilize a chemical feed pump to inject an oxidizing chemical, like chlorine, 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, like a manganese greensand filter. Excess chlorine can be removed by an activated carbon filter.

In some cases, the problem may only be eliminated by drilling a new well in a different place or connecting to an alternate water source if available.

Water heater

Follow the steps below if there is a problem with the water heater. Unless you are very familiar with the operation and maintenance of the water heater, you should contact a plumber to do the work.

1. Replace or remove the magnesium anode. 
   Many water heaters have a magnesium anode, which is attached to a plug located on top of the water heater. It can be removed by turning off the water, releasing the pressure from the water heater, and unscrewing the plug. Be sure to plug the hole. However, removal of the anode may significantly decrease the life of the water heater. A replacement anode may provide corrosion protection without contributing to the production of hydrogen sulfide gas. Contact a water heater dealer to find out if a replacement anode made of a different material, such as aluminum, can be installed.
2. Disinfect and flush the water heater with a chlorine bleach solution. 
   Chlorination can kill sulfur bacteria if done properly. If all bacteria are not destroyed by chlorination, the problem may return within a few weeks.
3. Increase the water heater temperature to 160°F for several hours. 
   This will destroy the sulfur bacteria. Flushing to remove the dead bacteria after treatment should control the smell.

CAUTION: Increasing the water heater temperature can be dangerous. Before you increase the temperature, consult with the manufacturer or dealer to make sure you know how to operate the pressure relief valve, and for other recommendations. After treatment, be sure to lower the thermostat setting and make sure the water temperature is reduced to prevent injury from scalding hot water and to keep energy costs low.

Funding is available to help you pay for water treatment or to fix your water system. Learn more about financial assistance programs and eligibility.