Dug Wells pose the highest risk of allowing drinking water supply contamination because they are shallow and often poorly protected from surface water. A dug well is a large diameter hole (usually more than 2 feet wide), which is often built by hand.

Bored Wells are constructed using an earth auger, usually up to 2 feet in diameter. Concrete is the most common casing material. These wells are typically hallow (less than 60 feet) and thus tend to be susceptible to surface contamination. These wells pose a moderate to high risk of contamination and are the first to go dry in a drought.

Driven point (sand point wells) - which pose a moderate to high risk, are constructed by driving assembled lengths of pipe into the ground. These wells are normally smaller in diameter (2 inches or less) and less than 50 feet deep. They can only be installed in areas of relativity loose soils, such as sand.

Drilled Wells cover all other types of wells, including those constructed by a combination of jetting and driving. Drilled wells fro farm use are commonly 4 to 8 inches in diameter and when properly constructed pose a relatively low risk of contamination.