People whose drinking water came from newer groundwater had a higher risk of developing Parkinson’s disease than those whose drinking water came from older groundwater, according to a preliminary study released March 2, 2026, that will be presented at the American Academy of Neurology’s 78th Annual Meeting taking place April 18–22, 2026, in Chicago and online.
The study does not prove that newer groundwater causes Parkinson’s disease; it only shows an association.
The research focused on the age of groundwater and the aquifers that supply it. An aquifer is an underground layer of porous rock, silt, or sand that stores and transports groundwater. Scientists increasingly see water sources as a window into long-term environmental exposures.
“One way to examine our exposure to modern pollution is through our drinking water,” said study author Brittany Krzyzanowski, PhD, of the Atria Research Institute in New York City, who conducted the research while at the Barrow Neurological Institute. “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.”
The study analyzed data from 12,370 people with Parkinson’s disease and more than 1.2 million people without the disease, matched for age, sex, race, and ethnicity. All participants lived within three miles of 1,279 groundwater sampling sites across 21 major U.S. aquifers.
A case for raw water from ancient sources
Researchers examined groundwater age, aquifer type, and drinking water source—such as municipal groundwater systems or private wells—as indicators of possible exposure to neurotoxic contaminants.
Two types of aquifers stood out. Carbonate aquifers, made mostly of limestone, often allow water to move quickly through fractures, making them more vulnerable to surface contamination. Glacial aquifers, formed more than 12,000 years ago as glaciers advanced and retreated, are composed of sand and gravel that can naturally filter water as it moves underground.
After adjusting for factors such as age, sex, income, and air pollution, people whose drinking water came from carbonate aquifers had a 24% higher risk of developing Parkinson’s disease compared with those whose water came from other aquifers. When compared specifically with people whose water came from glacial aquifers, the risk was 62% higher.
Researchers also found that older groundwater appeared to have a protective effect in carbonate aquifers. For each increase in groundwater age, the risk of Parkinson’s disease declined by about 6.5%. In contrast, groundwater formed in the past 75 years in carbonate systems was linked to an 11% higher risk compared to water dating back to the ice age.
“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,” she added.
The findings highlight how where drinking water comes from may matter for long-term health. People can often learn about their water source through local utilities or regional groundwater agencies. For households using private wells, testing water periodically and considering filtration systems can help reduce potential exposure to contaminants.
“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.”
