How can bacteria get into drinking water?

Coliform bacteria do not occur naturally in groundwater. However, coliform bacteria can live within slime formed by naturally occurring ground water microorganisms. The slime (or biofilm) clings to the well’s screen, casing, drop pipe, and pump. Disturbances during well construction, pumping or maintenance can cause the slime to dislodge, releasing the coliform bacteria into the water. The following can also lead to contamination:

  • Missing / defective well cap - seals around wires, pipes or where the cap meets the casing may be cracked 
  • Cracks or holes in the well casing - allow water that has not been filtered through the soil to enter the well (common in wells made of concrete, clay tile, or brick) 
  • Many older wells were not sealed with grout when constructed - allows contaminant to seep into well 
  • Well flooding - common problem for wellheads below ground in frost pits that flood during wet weather 
  • Close proximity of a well to septic tanks, drainfields, sewers, drains, privies, barnyards, animal feedlots, abandoned wells and surface water - contamination can enter the well 
  • Cross-connections with wastewater plumbing - wastewater can mix with the well water 

Show All Answers

1. How often should I test my well water for bacteria?
2. How do I test my well water for bacteria?
3. What should I do if coliform bacteria are detected in my well?
4. What do my test results mean?
5. How can I eliminate coliform bacteria from my well water?
6. How can bacteria get into drinking water?