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Mercury in Drinking Water - Frequently Asked Questions

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General information about mercury and its health effects

What is mercury and where does it come from?
Mercury is a liquid metal that occurs naturally in geologic formations and is released into the environment through various human activities. The major sources of mercury in drinking water are erosion of natural deposits, discharge from refiners and factories, and runoff from landfills and cropland. Electrical products such as dry cell batteries, fluorescent and ultraviolet (UV) light bulbs, switches and other control equipment account for a large percentage of mercury used.

When does mercury in drinking water become a health concern?
Under the Safe Drinking Water Act, the U.S. Environmental Protection Agency (EPA) determines the level of contaminants in drinking water at which no adverse health effects are likely to occur. This level is known as the maximum contaminant level (MCL). The MCL for mercury is 2 parts per billion (ppb). A public drinking water system must notify the public if its water has mercury levels above the MCL. The notice must explain how the water system plans to resolve the mercury contamination and that consumers can continue to drink water with mercury levels above the MCL in the short term.

How can mercury affect my health?
Mercury is primarily inorganic or elemental by nature when released into the environment. In this form, it is not considered harmful to human health at the levels typically found in drinking water. However, long term exposure to drinking water containing mercury well above the MCL can cause adverse health conditions, such as kidney damage.

Is mercury found in Oregon's drinking water systems?
Mercury is not commonly found in Oregon drinking water systems. Of the more than 3,400 active public drinking water systems in Oregon, only one system has ever found mercury levels greater than the MCL. This particular water system was last tested in 2005 and mercury was not detected.

Learning about mercury levels in your drinking water

For people on municipal or public water systems:
Public drinking water providers are required to monitor for mercury and ensure levels remain below the drinking water standard of 2 ppb. They are also required to make those results public. If your water comes from a public water system (i.e., you pay a water bill), you can find results on the Oregon Drinking Water Services Data Online website. Your drinking water provider may also be required to provide a Consumer Confidence Report to its customers every year. This report contains the most recent mercury test results if a detection has occurred within the past five years. Contact your drinking water provider for a copy of the most recent consumer confidence report.

For private well owners:
If your drinking water comes from your own well, contact an accredited laboratory that does water testing. These labs can provide information and instructions for well water testing. For a list of accredited laboratories in Oregon, contact the Oregon Environmental Laboratory Accreditation Program (ORELAP) or visit Oregon Drinking Water Services Laboratory Lists and Reporting Information.

Removing mercury from drinking water

For public drinking water system operators:
Mercury can be reduced below 2 ppb in drinking water using granular activated carbon filtration, coagulation/filtration, lime softening or reverse osmosis. The Oregon Health Authority (OHA) recommends that you work with an engineer to determine the most appropriate treatment for your system. Treatment has limitations and disadvantages. Not all kinds of treatment are effective, and no single treatment method can remove all contaminants from water. If treatment isn't possible for your system, you should consider developing a different water source or connecting to another safe water source in the area.

Water that is to be used for drinking, beverage-making or food preparation can be used on a temporary basis. Non-ingestion uses of water pose much less hazard, but might not be entirely safe if mercury levels are significantly above its drinking water MCL. Before deciding on treatment equipment, contact Oregon Drinking Water Services for information and advice.

For private well owners:
Several treatment options are available to remove mercury from well water. One of the most commonly used options is granular activated carbon filtration. OHA recommends either central (at the wellhead) treatment for multiple users or a point-of-entry (into the home) treatment in a private residence. Costs may be reduced with a point-of-use device (e.g., kitchen sink filter).

Treatment equipment must be carefully maintained in order to work properly and might not be effective if mercury levels are very high. Your contractor, engineer, or the system manufacturer should be able to help with this information. It is recommended that treated water be tested at least once a year. Untreated water should be tested at least every 3 years.

Make sure that any treatment system used is certified by a recognized, third-party testing organization that meets strict testing procedures established by the American National Standards Institute (ANSI) and National Sanitation Foundation (NSF) International.

Using mercury in drinking water system equipment

Where is mercury and how much is there?
Mercury can be found in electrical switches, sensors, gauges and meters for drinking water system equipment. Mercury levels in equipment range from a high of 5 kilograms in the mercury seals in water pumps to a low of 3 milligrams in low pressure UV light bulbs. The following scenarios are examples of how the mercury concentration in water could reach the MCL of 2 ppb:
  • 7.6 grams of mercury diluted in one million gallons of water;
  • 3 milligrams of mercury (the amount in a low pressure UV tube) diluted in 400 gallons of water;
  • 1 gram of mercury (the amount in a medium pressure lamp) diluted in 400,000 gallons of water.
To plan for worst case, for instance, consider how many tubes could break at once.

How can short-term exposure to mercury harm an operator's health?
Exposure to high levels of metallic mercury vapors can permanently damage the brain or kidneys.

Protecting operators and communities
Adopt best management practices to minimize spills and worker exposure to mercury-containing equipment and mercury vapors resulting from spills.
  • Purchase mercury-free replacement equipment.
  • Identify and label mercury-containing components.
  • Train staff in safe mercury management and spill clean-up processes.
  • Dispose of mercury according to hazardous waste regulations.
  • Keep fully stocked spill kits and personal protective equipment (PPE) at sites of mercury-containing equipment.

For more information

Updated: June 2012