SC By SCWS Team | February 2, 2026 | 12 min read
How to Shock Chlorinate a Well
Got a positive bacteria test? Don't panic—shock chlorination is the solution. This proven method uses a high concentration of chlorine to kill bacteria, viruses, and other microorganisms in your well. When done correctly, shock chlorination is safe, effective, and something most homeowners can do themselves. This guide walks you through every step.
⚠️ Before You Start
- • Do not drink well water until you complete this process AND get a clear bacteria retest
- • Use bottled water or boil water until disinfection is confirmed successful
- • This process requires 12-24 hours without water use
- • Plan accordingly—stock up on water before starting
When to Shock Chlorinate Your Well
Shock chlorination is appropriate in these situations:
Positive Bacteria Test
Total coliform or E. coli detected in water sample
After Flood or Surface Water Entry
Contamination from runoff or high water table
After Well Repairs
Pump replacement, casing work, or any time well was opened
New Well Construction
Before first use to ensure clean water delivery
Extended Non-Use
Vacation home or property that sat unused for months
Off Odors or Tastes
Earthy, musty, or unusual smells suggesting bacterial growth
What You'll Need
Supplies
Chlorine Source:
- Unscented household bleach (5.25-8.25% sodium hypochlorite)
- OR calcium hypochlorite granules (pool shock)
- Calculate amount based on well size (see below)
Equipment:
- Clean 5-gallon bucket
- Garden hose (clean)
- Funnel (optional)
- Wrench for well cap
Safety Equipment:
- Chemical-resistant gloves (rubber or nitrile)
- Safety glasses or goggles
- Old clothes (bleach will damage fabric)
🚫 Do NOT Use
- • Scented bleach (contains fragrances)
- • "Splash-less" bleach (contains thickeners)
- • Bleach with added cleaners (surfactants)
- • Color-safe bleach (not chlorine-based)
- • Only use PLAIN, UNSCENTED household bleach
Calculating Chlorine Amount
The amount of chlorine needed depends on your well's water volume. Use this formula or the table below:
📐 Quick Calculation
For standard 5.25% household bleach in a 6-inch diameter well:
3 pints of bleach per 100 feet of water depth
(Water depth = Total well depth minus static water level)
Chlorine Amount by Well Size
| Well Casing Diameter | Water Depth | Bleach (5.25%) | Pool Shock (65%) |
|---|---|---|---|
| 4 inches | 100 feet | 1.5 pints | 2 oz |
| 6 inches | 100 feet | 3 pints | 4 oz |
| 6 inches | 200 feet | 6 pints | 8 oz |
| 6 inches | 300 feet | 9 pints | 12 oz |
| 8 inches | 100 feet | 5 pints | 7 oz |
| 8 inches | 200 feet | 10 pints | 14 oz |
Not sure of your well dimensions? Check your well drilling log for casing diameter and depth, or measure the static water level yourself.
Step-by-Step Procedure
Step 1: Bypass Water Treatment Equipment
Before starting, bypass or protect water treatment equipment:
- Water softener: Put in bypass mode or close valves
- Carbon filters: Bypass—chlorine will damage the carbon
- UV systems: No bypass needed, but the lamp won't be effective with chlorine present
- Reverse osmosis: Bypass if possible; chlorine may damage membranes
Step 2: Remove the Well Cap
Locate your well casing (usually a 4-8 inch pipe sticking up from the ground or in a well pit) and remove the sanitary cap:
- Loosen bolts or set screws securing the cap
- Carefully lift off the cap
- Note how wires and pipes are routed for reassembly
- Set cap aside in clean location
Step 3: Mix and Add Chlorine
- Mix initial solution: Add about half your calculated bleach amount to a 5-gallon bucket filled with water from a garden hose (not well water)
- Pour into well: Carefully pour the chlorine solution into the well casing
- Add remaining bleach: Pour remaining bleach directly into the well
- Rinse bucket: Fill bucket with clean water and pour down well to rinse all chlorine in
⚠️ Safety Warning
Chlorine is corrosive. Wear gloves and eye protection. If bleach contacts skin, rinse immediately with water. Do not mix bleach with any other chemicals—toxic gases can result.
Step 4: Recirculate Water in the Well
This critical step distributes chlorine throughout the well:
- Connect garden hose: Attach hose to an outdoor faucet (not run through water treatment)
- Insert hose into well: Lower the hose end into the well casing, past the pitless adapter if possible
- Turn on water: Run the pump so water circulates through the hose and back into the well
- Wash down casing walls: Move the hose around to rinse the entire interior of the casing
- Continue 15-30 minutes: Until you smell strong chlorine odor coming from the well
Step 5: Run Chlorine Through House Plumbing
Now distribute chlorinated water throughout your plumbing system:
- Open each cold water faucet: One at a time, until you smell chlorine, then close
- Open each hot water faucet: Same procedure—this treats the water heater
- Flush toilets: Refill tanks with chlorinated water
- Run outdoor faucets: Until chlorine odor is present
- Don't forget: Washing machine connections, refrigerator water line, ice maker
The goal is to have chlorinated water in every part of the plumbing system.
Step 6: Wait for Contact Time
⏱️ Contact Time Is Critical
Allow chlorinated water to sit in the system for at least 12-24 hours. Do not use any water during this time. Longer contact time (up to 48 hours) is more effective for stubborn contamination.
During the waiting period:
- Do not run any water
- Replace the well cap (loosely, to allow gas escape)
- Use stored bottled water for drinking and cooking
- Plan for no showers, laundry, or dishwashing
Step 7: Flush the System
After contact time, remove the chlorinated water:
- Flush outdoors first: Connect a garden hose and run water to an area away from plants and septic (chlorine can damage both)
- Run until no chlorine smell: This may take 30 minutes to several hours depending on well volume
- Then flush indoor plumbing: Run each faucet until chlorine odor is gone
- Flush water heater: Run hot water faucets until clear and chlorine-free
- Return treatment equipment to service: Take water softener, filters off bypass
💡 Flushing Tips
- • Direct flush water away from garden plants—chlorine damages vegetation
- • Avoid flushing large volumes into septic system—discharge outdoors when possible
- • If you have a lawn area far from garden, that's a good discharge point
- • Chlorine dissipates naturally—wait a few days before watering plants in that area
Step 8: Retest Water
The job isn't done until you confirm success:
- Wait 7-14 days: Bacteria testing immediately after chlorination may give false negatives
- Collect sample properly: Use lab-provided container, follow instructions exactly
- Submit to certified lab: Home test kits aren't adequate for this—see testing kit vs lab
- Test for total coliform and E. coli: Both should be absent
If Bacteria Returns
If your retest shows bacteria again, there's likely an ongoing contamination source. Common causes include:
Damaged or Missing Well Cap
Allows insects, debris, and surface water to enter. Replace with proper sanitary cap.
Failed Sanitary Seal
Grout seal around casing has cracked or deteriorated, allowing surface water in.
Casing Damage
Cracks or holes in the well casing, especially near surface. May need video inspection.
Septic System Problems
Septic too close to well, failed drain field, or improperly sealed well creating pathway.
Surface Water Intrusion
Well is in low area where surface water collects, or grading directs water toward well.
If bacteria returns after chlorination, professional investigation is needed. A well video inspection can identify casing problems, and a thorough evaluation of the wellhead area can find surface contamination pathways.
Professional vs DIY Chlorination
While shock chlorination is a DIY-able task, consider professional help if:
- You're uncomfortable working with chemicals
- The well cap is difficult to access or remove
- You've tried chlorination before without success
- You suspect a structural problem with the well
- You want guaranteed results with follow-up testing
Professional chlorination typically costs $150-$400 and includes proper dosing, thorough distribution, and often follow-up testing. Learn more about well chlorination costs.
Frequently Asked Questions
How much chlorine do I need to shock my well?
A general rule is 3 pints of standard household bleach (5.25% sodium hypochlorite) per 100 feet of water depth in a 6-inch diameter well. For higher-strength bleach or different well diameters, amounts vary. Target a chlorine concentration of 100-200 ppm in the well water.
How long should chlorine stay in the well?
Allow the chlorinated water to remain in the well for at least 12-24 hours. Longer contact times (up to 48 hours) are more effective for stubborn contamination, but most sources recommend a minimum of 12 hours.
When should I shock chlorinate my well?
Shock chlorinate when: a bacteria test comes back positive, after any well repairs or pump replacement, after flooding or surface water intrusion, if water develops off odors or tastes, or when the well has been unused for extended periods.
Can I use pool chlorine to shock my well?
Pool chlorine (calcium hypochlorite) can be used but requires careful calculation due to its higher concentration (typically 65-70%). Household bleach is easier to measure. Never use bleach with added fragrances, surfactants, or thickeners.
Will shock chlorination harm my septic system?
Large amounts of chlorine can temporarily disrupt septic system bacteria, but a single shock chlorination typically doesn't cause lasting damage. Minimize impact by flushing chlorinated water outdoors rather than into the septic system when possible.
What if bacteria comes back after shock chlorination?
If bacteria returns shortly after chlorination, there's likely an ongoing contamination source: damaged casing, failed sanitary seal, surface water intrusion, or cross-contamination from septic. Professional investigation is needed to identify and fix the source.
Need Help With Well Disinfection?
Whether you want professional chlorination, need help after a failed DIY attempt, or have ongoing bacteria problems requiring investigation, our technicians can help. We serve well owners throughout San Diego County with complete disinfection services.
