Complete Guide to Shock Chlorination for Water Wells
Protect your family's health with this comprehensive guide to eliminating bacteria from your well water through proper shock chlorination.
Protect your family's health with this comprehensive guide to eliminating bacteria from your well water through proper shock chlorination.
Shock chlorination is a one-time, high-dose chlorination process used to disinfect wells and plumbing systems that have become contaminated with bacteria. Unlike the continuous low-level chlorination used in municipal water systems, shock chlorination uses a much higher concentration of chlorine to eliminate harmful microbes throughout your entire water system. This proven method is your first line of defense when bacteria tests come back positive, after well servicing, or following contamination events. This guide provides everything you need to safely and effectively disinfect your well, from calculating the right chlorine dose to knowing when professional help is needed.
Knowing when to disinfect is critical for maintaining safe drinking water. The EPA and health departments recommend shock chlorination in these specific situations:
If water testing reveals coliform bacteria or E. coli, immediate shock chlorination is essential. Even a single detection indicates potential contamination that must be eliminated.
Any time your well is opened for pump installation, repairs, or maintenance, bacteria can enter. Always disinfect after well work to ensure system safety.
If flood waters or heavy runoff have reached your wellhead, or if water turns muddy after storms, shock chlorination is necessary to eliminate surface contaminants.
Sudden changes in taste, odor, or appearance can indicate contamination. Iron bacteria causing slime or sulfur odors may temporarily improve with shock treatment.
Shock chlorination involves strong chemicals and potential hazards. Protecting yourself and your equipment is essential for a successful treatment.
Use this guide to determine the correct amount of chlorine for your well. Using the proper amount ensures effective disinfection without waste or equipment damage.
| Water Depth (ft) | 4″ Well | 6″ Well | 8″ Well | 10″ Well | 12″ Well |
|---|---|---|---|---|---|
| 10 | ½ cup | 1 cup | 1½ cups | 2 cups | 1 quart |
| 25 | 1 cup | 2 cups | 1 quart | 1½ quarts | 2¼ quarts |
| 50 | 2 cups | 1 quart | 2 quarts | 3 quarts | 1 gallon |
| 100 | 1 quart | 2 quarts | 1 gallon | 1½ gallons | 2 gallons |
| 150 | 1½ quarts | 3 quarts | 1½ gallons | 2 gallons | 3 gallons |
Note: Always round up to the next higher amount. Never exceed recommended amounts significantly—more chlorine won't disinfect better but will be harder to flush and may corrode components.
Turn off power to the pump. Remove the well cap carefully. Mix the calculated amount of chlorine with 5-10 gallons of water. Pour the mixture into the well casing. If using dry chlorine, always dissolve it first.
Replace the well cap and turn the pump back on. Connect a hose to an outdoor faucet and run water back into the well until you smell chlorine. Then run water at each indoor faucet until chlorine odor is detected.
Turn off the pump and let the chlorinated water sit in the system. Ideal contact time is overnight to 24 hours. Do not use any water during this period. Post signs to remind household members.
Start with outdoor faucets, directing water away from plants and septic systems. Run until chlorine smell disappears. Then flush each indoor fixture thoroughly. This may take several hours and hundreds of gallons.
Wait 5-10 days after flushing, then collect a water sample for bacteria testing. Do not drink the water until test results confirm no coliform bacteria or E. coli. Retest after 2-4 weeks to ensure continued safety.
You should shock chlorinate if: (1) A water test shows positive for coliform bacteria or E. coli, (2) After any well service like pump replacement or repairs, (3) Following flooding or if surface water has entered the well, (4) If you notice changes in water taste, odor, or appearance. Even a single detection of bacteria indicates the need for immediate disinfection.
The amount depends on your well's diameter and water depth. For example, a 6-inch diameter well with 50 feet of water needs about 1 quart of unscented household bleach (5-6% sodium hypochlorite). Never use scented or 'splashless' bleach. Always round up when calculating – it's better to slightly overdose than underdose.
The ideal contact time is 12-24 hours. At minimum, leave chlorinated water in the system for 8 hours, but overnight (12 hours) is recommended. Maximum contact time should not exceed 24 hours as prolonged exposure can corrode metal components and potentially mobilize contaminants like arsenic in some aquifers.
No. After completely flushing all chlorine from your system, wait 5-10 days before collecting a water sample for bacteria testing. Only resume drinking the water after receiving negative test results for coliform bacteria and E. coli. The waiting period allows any residual chlorine to dissipate completely.
Recurring bacteria indicate a persistent contamination source that shock chlorination alone won't fix. This could be a cracked well casing, improper seal, inadequate well cap, or nearby pollution source like a failing septic system. Contact a licensed well contractor to inspect for structural problems and consider installing a continuous disinfection system.
Yes, if you follow proper safety procedures: wear rubber gloves, goggles, and protective clothing; ensure adequate ventilation; turn off power to the pump before opening the well; use only plain chlorine products. However, if you're uncomfortable with the process or have recurring contamination, hire a licensed well professional.
Shock chlorination is a temporary solution. Contact a licensed well contractor if:
Remember: Your family's health is the top priority. When in doubt, consult a professional.
Shock chlorination is a proven, effective method for eliminating bacterial contamination from your well. By following proper procedures, using correct dosages, and testing to verify results, you can restore your water quality and protect your family's health. Remember to test annually and after any contamination events to maintain safe drinking water.