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Molybdenum in groundwater

Molybdenum (Mo) is a metallic element that is naturally present, usually at low levels, in the earth’s crust. Trace amounts of molybdenum are necessary for human health, and are obtained from common foods in the diet such as leafy vegetables, legumes, grains and organ meats. Higher concentrations have been found in soil or groundwater, typically in conjunction with spills or some historic waste disposal practices. Residents are advised to avoid the extremely low risk associated with future molybdenum exposures by not consuming water that contains molybdenum above the Wisconsin health advisory level of 90 micrograms per liter (μg/L). Naturally-occurring levels of molybdenum in groundwater are low; U.S. Geologic Survey found a median value of 1 μg/L nationwide. Most well owners do not need to include molybdenum during annual well testing.

Molybdenum in southeast Wisconsin

Molybdenum concentrations above the state health advisory level were found in monitoring wells and private water supply wells in southeast Wisconsin. A two-year DNR study was unable to determine the origin of the elevated levels of molybdenum.

Who should test

The department, along with the state Department of Health Services (DHS) and local health officials, recommend that residents using private wells in sections with molybdenum results at 90 or greater and adjacent sections should sample and test their well water for molybdenum. This testing can be done along with recommended annual testing for bacteria and nitrates. Testing cost ranges from $13 to $45.

Testing your well water

Contact a certified laboratory that can test your water for a specific contaminant.
Collect a water sample properly

The laboratory you work through will provide you with a water sampling kit. You can watch a demonstration showing basic methods for properly collecting a water sample to yield accurate results.

Health information

Staff at DHS completed a comprehensive review of molybdenum health studies. If you have molybdenum in your drinking water, this information can help you decide whether you need to seek an alternative supply of drinking water.


The Department of Safety and Professional Services (DSPS) has approved water treatment devices for molybdenum and boron. The total device cost ranges from $400 to $1000 depending on model and labor.

Water treatment devices
DSPS products register:, choose plumbing products, then from the Select Credential/Permit Type dropdown choose water treatment device.

A licensed pump installer, well driller or similar water industry professional should be hired to correctly install an appropriate treatment device.

More information

Molybdenum in southeast Wisconsin Jesse Jensen
Drinking water, wells and well testing Greg Roanhouse
Caledonia Groundwater Molybdenum Investigation Joe Lourigan
Molybdenum health issues Sarah Yang
Dept. of Health Services (DHS)
Molybdenum treatment Glen Schlueter
Dept. of Safety & Professional Services (DSPS)


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