Molybdenum In Groundwater
Molybdenum (Mo) is a metallic element that is naturally present, usually at low levels, in the earth's crust. Small 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. Naturally-occurring levels of molybdenum in groundwater are typically low; the U.S. Geologic Survey found an average of 1 microgram of molybdenum per liter of water (μg/L) nationwide. However, higher levels have been found in soil or groundwater due to natural geologic conditions, or spills and historic waste disposal practices.
Drinking Water Health Advisory Level for Molybdenum
In 2026, the Wisconsin Department of Health Services (DHS) updated its drinking water health advisory level for molybdenum from 90 micrograms per liter (µg/L) to 200 µg/L. Exposure to high levels of molybdenum can affect kidneys and may cause liver damage and impact reproduction. Learn more at DHS molybdenum in drinking water.
Wisconsin currently has NR 140 groundwater standards for molybdenum with a preventative action limit (PAL) of 8 µg/L and an enforcement standard of 40 µg/L. These regulatory groundwater standards have not changed and remain in effect. The Wisconsin Department of Natural Resources (DNR) and the DHS will continue to coordinate their response to molybdenum detections in private wells and provide health-based recommendations to well owners using the updated DHS health advisory level.
Molybdenum In Southeast Wisconsin
Molybdenum concentrations above the previous state drinking water health advisory level of 90 µg/L were found in monitoring wells and private water supply wells in southeast Wisconsin. A two-year DNR study (2011 - 2013) was unable to determine the origin of the elevated levels of molybdenum.
- Caledonia Groundwater Molybdenum Investigation (WA-1625)
- Summary of the DNR's Molybdenum and Boron Investigation (WA-1640)
Who Should Test
The DNR and DHS recommend that private well users in municipalities with molybdenum results at 200 μg/L or greater test their well water for molybdenum at least once. This testing can be done along with recommended annual testing for bacteria and nitrates. Most well owners do not need to include molybdenum during annual well testing. Learn more at the DHS website.
The following municipalities had at least two molybdenum sample results over 200 (μg/L):
Belvidere, Bristol, Pacific, Waukesha and Wilson.
Testing your well water
Contact a certified laboratory that can test your water for a specific contaminant.
How To Properly Collect A Water Sample
The laboratory you work through will provide you with a water sampling kit. The video below is demonstration showing basic methods for properly collecting a water sample to yield accurate results.
Water Treatment Devices
Distillation and Reverse Osmosis can be effective at reducing molybdenum concentration in water.
A licensed pump installer, well driller or similar water industry professional should be hired to correctly install an appropriate treatment device.
Contacts
| Molybdenum in southeast Wisconsin | Jesse Jensen 414-263-8774 |
| Drinking water, wells and well testing | Greg Roanhouse 262-884-2356 |
| Caledonia Groundwater Molybdenum Investigation | Mark Peters 608-516-0820 |
| Molybdenum health issues | Dept. of Health Services (DHS) 608-264-9829 |
| Molybdenum treatment | Glen Schlueter Dept. of Safety & Professional Services (DSPS) 608-267-1401 |