How to Shock Chlorinate a Well (Step by Step)

Shock chlorination kills bacteria in your well and plumbing. It's the standard step after a positive coliform test, a flood, well repairs, or sulfur and iron bacteria problems.

By Haroon Updated How we research
Safety: wear gloves and eye protection, and never mix bleach with other cleaners. Turn off power before opening a well cap that has wiring. With a flooded pump, have the electrics checked first. If you're unsure, a licensed well contractor can do this, and that's often best for deep drilled wells.

When to shock chlorinate

Step 1: Work out how much water is in your well

Water volume = feet of water in the well × gallons per foot for your casing size. Your well record may list the depth and static water level.

Casing diameterGallons per foot of water
2 in0.16
4 in0.65
6 in1.47
8 in2.61
Example: a 6-inch well, 200 ft deep, water level at 50 ft → 150 ft of water × 1.47 = about 220 gallons in the well.

Then use the bleach amount from the dose chart in Penn State's shock chlorination guide, or your state health department's, for that volume and your bleach strength. Don't guess: too little doesn't work, and far too much is hard to flush.

Step 2: Prepare

  1. Bypass or turn off water treatment equipment (softeners, filters, UV), unless the maker says otherwise.
  2. Have bottled water ready for 1–2 days.
  3. Clean around the wellhead and remove debris.

Step 3: Chlorinate

  1. Mix the measured unscented bleach with several gallons of water and pour it into the well.
  2. Connect a hose to an outdoor tap and run it back into the well to recirculate, rinsing the inside of the casing, until you smell chlorine at the hose.
  3. Open every tap in the house, hot and cold, one at a time, until you smell chlorine, then close it. Flush toilets too.
  4. Let the chlorinated water sit. South Carolina's guidance says to wait 6–24 hours; many guides say 12–24.

Step 4: Flush

  1. Run an outdoor hose away from plants, streams and the septic field until the chlorine smell is gone.
  2. Then run indoor taps briefly to clear them.
  3. Put treatment equipment back in service, following its own sanitizing instructions.

Step 5: Retest

Test for total coliform and E. coli 7–10 days later, once there's no chlorine left, and again a few months later. Georgia's guidance notes flooded wells may need repeated testing for months.

Coming back positive again? The contamination source isn't fixed. Check the cap, casing and septic distance, and consider UV for ongoing protection.

Frequently asked questions

How do you shock a water well?

Work out how much water is in the well, add the right amount of unscented bleach, recirculate it with a hose until you smell chlorine, run every tap, let it sit 6 to 24 hours, flush outdoors, then test for bacteria 7 to 10 days later.

Can I bleach my water well myself?

Yes, many homeowners do, following a state or extension procedure. For deep drilled wells, flooded wells or wiring near the wellhead, a licensed well contractor is often the safer choice.

How long after shock chlorinating can I drink the water?

Not until the chlorine has been flushed out and a bacteria test comes back clean. South Carolina’s guidance suggests testing 7–10 days after disinfection. Use bottled or boiled water until then.

Can I use any bleach?

Use plain, unscented household bleach with no additives (no “splash-less”, scented or thickened products). Check the label for the chlorine percentage, because dose charts depend on it.

Will shock chlorination fix my water permanently?

It kills bacteria in the well and plumbing at that moment. If contamination keeps getting in (bad cap, cracked casing, nearby septic), it will come back. Fix the source.

Can I flush chlorinated water into my septic system?

Avoid it. Large amounts of chlorinated water can harm the septic system’s bacteria. Flush through an outdoor hose to an area away from plants, streams and the septic field.

Sources

  1. Shock Chlorination of Wells and Springs, Penn State Extension
  2. Private Well Fact Sheet (flooding), South Carolina Department of Environmental Services
  3. What to Do After a Flood: Water Wells, Georgia Department of Public Health
  4. Private Well Flood Guidance, Tennessee Department of Health
  5. Iron Bacteria in Well Water, Minnesota Department of Health
  6. Private Drinking Water Wells, U.S. EPA

Sources checked October 24, 2026. Found an error? Tell us and we will fix it.

Haroon, Founder and editor
Writes The Well Owner from public-health and university extension sources. Every number on this page links to where it came from. More about us.