There are a number of steps that a homeowner can take to help protect their private well.
Water should be diverted away from the wellhead to prevent the pooling and potential introduction of contaminated water into the well.
Keep the well in good repair. A faulty well can allow surface water to reach groundwater without filtering through the soil.
Use care when applying pesticides and fertilizers to lawns and gardens near the well (better yet, avoid use entirely if possible). These products contain chemicals and/or nutrients that can contaminate well water.
Abandoned wells should be sealed. They are a prime entryway for contaminants.