Well water can be contaminated by surface water if there are:

• Openings in the well seal;
• Improperly installed well casing;
• Well casing not deep enough;
• Well casing not sealed. 

Contamination from surface water can come from a number of sources:

• Any chemical or fuel spills that infiltrates the ground can contaminate your drinking water source.
• Fertilizers and pesticides typically used in gardens should not be applied on the same property as a well, as they present a major potential source for contamination.
• Underground storage tanks and associated pipes can leak, especially if they are 15 years or older. Underground tanks present a special concern if the water table is shallow or if the tank is close to your well.
• Livestock and pet wastes are a serious potential threat to well water. Wastes should be contained and properly disposed of, do not allow for the waste to be washed away with rain water.

Most polluted well water is caused by contamination sources being located too close to the well, by improper well construction or operation, or by inadequate well maintenance.

Learn more about surface water contaminants at Well Aware and Health Canada's What's in Your Well?