A new study has found a link between the age of groundwater used for drinking and the risk of developing Parkinson's disease. The research, which will be presented at the American Academy of Neurology's 78th Annual Meeting in April 2026, analyzed data from more than 12,000 people with Parkinson's and over 1.2 million people without the disease across the United States.
The study focused on groundwater age and the types of aquifers supplying drinking water. Aquifers are underground layers that store and transport groundwater, with carbonate aquifers (mainly limestone) being especially common in parts of the Midwest, South, and Florida, while glacial aquifers are mostly found in the Upper Midwest and Northeast.
"One way to examine our exposure to modern pollution is through our drinking water," said Brittany Krzyzanowski, PhD, of Atria Research Institute in New York City. She conducted this research while at Barrow Neurological Institute in Phoenix, Arizona, and is a member of the American Academy of Neurology. "Newer groundwater, created by precipitation that has fallen within the past 70 to 75 years, has been exposed to more pollutants. Older groundwater typically contains fewer contaminants because it is generally deeper and better shielded from surface contaminants. Our study found that groundwater age and location is a potential environmental risk factor of Parkinson's disease."
Researchers evaluated whether participants' drinking water came from municipal systems or private wells using different aquifer types. They adjusted for factors such as age, sex, income level, and air pollution.
Findings showed that people whose drinking water came from carbonate aquifers had a 24% higher risk of developing Parkinson's compared to those using other aquifer types. The risk was even higher—62%—when compared specifically to those whose water came from glacial aquifers.
The protective effect against Parkinson’s was linked only to older groundwater sourced from carbonate aquifers. For every standard deviation increase in groundwater age in these systems, there was about a 6.5% decrease in Parkinson’s risk. Conversely, newer groundwater (less than 75 years old) from carbonate systems was associated with an 11% higher risk compared to much older groundwater (over 12,000 years old).
"We speculate that the apparent protective effect of older groundwater is seen mainly in carbonate aquifers because these systems can show a clearer contrast between newer and older water," said Krzyzanowski. "In these aquifers, newly recharged groundwater is more vulnerable to surface contamination, while older groundwater can remain cleaner if it is separated from recent inputs by a confining layer."
"In contrast, glacial aquifers tend to slow groundwater movement and naturally filter contaminants as water travels underground," said Krzyzanowski. "As a result, differences in contamination between newer and older groundwater in these aquifers may be smaller and therefore harder to detect."
Krzyzanowski added that residents can usually find information about their drinking water source through local utilities or state or county resources for private wells.
"This study highlights that where our water comes from, including the age of groundwater and the type of water source, could shape long‑term neurological health," said Krzyzanowski. "While additional research is needed, bringing together knowledge about groundwater and brain health may help communities better assess and reduce environmental risks."
The researchers noted one limitation: they assumed all individuals living within three miles of a sampling site shared similar aquifer characteristics.
The study received support from several organizations including AAN Clinical Research Training Scholarship, American Brain Foundation and The Parkinson's Foundation.
