How to Shock a Well: A Homeowner’s Guide to Disinfecting Your Water Supply

Private wells offer clean, reliable water to millions of homes — especially in rural areas across Central New York. But unlike municipal water systems, private wells are not automatically treated or monitored. Bacteria can enter through the well cap, groundwater, plumbing repairs, or seasonal flooding, putting homeowners at risk for contamination.One of the most common and effective maintenance treatments is well shocking, also called well disinfection, which uses chlorine to sanitize the well, plumbing lines, and pressure tank.

When Should a Well Be Shocked?

A well should be disinfected when:

✔ A water test can detect coliform and/or E. coli bacteria

✔ After plumbing repairs or pump replacement

✔ After flooding or heavy runoff infiltration

✔ If the well cap was left open

✔ When the water has a persistent odor or slime buildup

Routine testing is recommended at least once a year for homeowners on private wells.

What You’ll Need

Before shocking a well, gather:

• Unscented household bleach (5–8.25% sodium hypochlorite)
• A clean 5-gallon bucket
• Protective gloves and eyewear
• Garden hose
• Access to outdoor faucets
• Water test kit (optional but recommended afterward)

Step-by-Step: How to Shock a Well

1. Bypass Water Treatment Systems

Temporarily bypass filters, softeners, RO units, and carbon tanks — chlorine can damage media and membranes.

2. Calculate the Correct Chlorine Amount

As a general guideline:

1–2 gallons of unscented bleach will treat a standard 6" residential well, 100–200 ft deep

Deeper or larger diameter wells require more

3. Turn Off Power & Remove Well Cap

Shut off the pump breaker for safety, remove the cap, and pour the measured bleach into the well casing.

4. Mix & Recirculate

Turn the pump breaker back on and use a garden hose to run water back into the well for 10–15 minutes, mixing the bleach throughout the casing.

5. Bring Chlorinated Water to the House

Open interior faucets one at a time until you smell chlorine, then shut them off. Do the same for outdoor spigots. This step disinfects the pressure tank and distribution plumbing.

6. Let It Sit

Allow the chlorinated water to remain in the system for 8–12 hours, or overnight for best results.

7. Flush the System

Flush outdoors, away from grass and septic fields, until the chlorine odor dissipates.

Then open indoor faucets and rinse until the smell is gone.

After the Shock — Retest the Water

Once flushing is complete, water quality should be retested in 7–10 days.

If bacteria remain present, a second shocking may be necessary — persistent failures may indicate:

• surface infiltration
• cracked well casing
• failed sanitary seal
• contaminated aquifer
• septic proximity issues

Important Safety Notes

⚠ Never use scented bleach or splashless bleach — additives can contaminate wells

⚠ Do not shock while on a shared well system without neighbor coordination

⚠ Avoid flushing chlorine into septic systems when possible

⚠ Children, pregnant individuals, and immunocompromised residents should avoid drinking water until testing is clear