Some well types and water sources are more susceptible to contamination than others.

Two major types of aquifers exist. "Confined" aquifers are protected from surface contamination by a layer of low permeability material (silt, clay or till). "Unconfined" aquifers do not have an impermeable layer overlying and protecting the aquifer and therefore are more vulnerable to surface contamination (the contaminants can infiltrate into the ground and reach the aquifer). In the Comox Valley eight of the fifteen know aquifers are classified as vulnerable to contamination.

Water is "cleaned" naturally (through filtration and biological processes) as it flows through the soil. However the amount of contaminants removed by this process depends on the type of soil, the type of contaminant, and the distance the water travels before reaching the water table. Water moves quickly through coarse soils (such as sand and gravel) and therefore these soils remove fewer contaminants. Water moves more slowly through fine-textured soil (such as peat, clay and silt) and therefore these soils are more effective at removing contaminants before they reach the groundwater

There are three types of wells: drilled, driven, and dug.