If you are one of the many residents in Big Sky who relies on a private well for your drinking water, here is something you should be aware of: unlike municipal water systems, no government agency is testing your water for you. The Environmental Protection Agency regulates public water supplies, but private wells fall outside that safety net entirely. That responsibility belongs to you—and it’s one of the simplest, most affordable things you can do to protect your family’s health.
Why Annual Testing Matters
Groundwater is far from static—it shifts year to year, influenced by population growth, landscaping practices, septic systems, road salt, precipitation events, and other contaminants that make their way from the ground or roadways into the aquifer. Substances like nitrates, bacteria (including E. coli and coliform), arsenic, and lead can seep into well water slowly, often with no detectable change in taste, smell, or appearance. That means you could be consuming contaminated water for months, even years, without ever realizing it.
This video shows how water moves through our septic systems and groundwater.
In 2025, the Montana Bureau of Mines and Geology Ground Water Investigation Program released findings from a study that examined groundwater flow dynamics, interactions with the Gallatin River, and the potential for pollution from septic systems to impact the river’s health. Not surprisingly, the study found that in developed areas west of the Gallatin, nitrate concentrations were more elevated than those in undeveloped areas east of the river. Concentrations ranged from 1.87mg/L – 5.84 mg/L. EPA drinking water standards come in at 10 mg/L, as above 10 mg/l can be lethal to infants. The higher than ideal levels at several wells throughout the Upper Gallatin Aquifer most likely reflects the influence of septic effluent, horse feedlots, or over-applied fertilizers, which all have the ability to infiltrate contaminants into the aquifer.
Nitrate contamination is an especially relevant concern locally, given how common septic systems, horse manure, and fertilizer applications are in our area. Infants and pregnant women face the greatest risk from elevated nitrate levels, though the health effects can accumulate for anyone over time. Bacterial contamination poses a different threat—often causing acute gastrointestinal illness—and tends to spike after flooding, heavy spring runoff, or when wells sit near septic systems or piles of horse manure.
What to Test For
At a minimum, well owners should test annually for:
- Total coliform bacteria and E. coli
- Nitrates
- pH and total dissolved solids
The first time you test your well—or anytime you notice changes in water quality, taste, or color—it’s also worth expanding the panel to include arsenic, lead, manganese, and other heavy metals.
It’s Not Just About Your Health
Testing your well is not just a personal health precaution—it is a way of looking after the Gallatin River and the smaller creeks that run through our community. If shared—there is an option to share your well data during the testing process—well data can provide a clearer picture of groundwater trends across the community, can help flag emerging contamination sources, and supports efforts to protect the aquifers that feed our rivers and streams.
Getting Started
Testing is inexpensive and straightforward. We are happy to connect you with resources, like the Well Educated program based at Montana State University.
Your well is your drinking water source—make sure it’s a safe one.
Pick up your free well testing kit at the Gallatin River Task Force office at 1700 Lone Mountain Trail in Big Sky, or reach out if you have questions about well testing or groundwater health in Big Sky area. We are here to help.
