How to Shock Chlorinate a Well, Step by Step

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Affiliate disclosure: Private Well Guide (privatewellguide.com) earns a commission from some links on this page, at no extra cost to you. We haven’t disinfected wells ourselves. The steps below summarize the CDC and University of Georgia Extension instructions. Follow those official pages, and your health department’s advice, over this summary. As an Amazon Associate I earn from qualifying purchases.

Safety and health note: CDC recommends that wells be disinfected by a well or pump contractor because of safety risks such as electric shock and toxic gases in well pits. Check with your local health department first. Shock chlorination doesn’t make water safe by itself. Only a follow-up lab test can show whether bacteria are gone.

When to shock chlorinate

UGA Extension and Penn State Extension recommend it:

  • After a new well is built or an unused well is returned to service
  • After a positive bacteria test
  • After the well is opened for installation, repair or maintenance (for example, a new pump)
  • When floodwater has surrounded or covered the well casing
  • When the water turns muddy or cloudy after rain
  • When there are signs of iron or sulfur bacteria (slime, odor)

When it’s not enough: UGA says shock chlorination is “NOT a recommended method for treating recurring bacteria problems.” Find and fix the source with a licensed well contractor, or install continuous disinfection. A Penn State study found shock chlorination plus a sanitary cap kept bacteria away for a year in only 15% of contaminated wells (Penn State). Coliform and E. coli in Well Water: What a Positive Test Means

Before you start: safety

From CDC and UGA:

  • Turn off power to the pump before removing the well cap or clearing debris. After a flood, have an electrician or well/pump contractor check the wiring before turning the power back on.
  • Never enter a well pit. Gases can build up.
  • Wear goggles or a face shield, rubber gloves and boots, and work in a well-ventilated area.
  • Arrange another drinking water source. No one should drink or bathe in the water until the process is finished. UGA says no one should use the water for any purpose during the 12–24 hour contact time.
  • Protect treatment equipment. CDC says to close valves to (bypass) water softeners. UGA says to disconnect carbon filters and reverse osmosis units, and to check with manufacturers about other equipment.
  • If your water smells of fuel or chemicals, stop. CDC warns that disinfection won’t make that water safe. Contact your health department.
  • Arsenic areas: UGA notes that shock chlorination can temporarily raise arsenic in some aquifers. Test for arsenic afterward if you have detectable arsenic.

What you need

  • Plain, unscented household liquid chlorine bleach. CDC notes concentrations are generally 5–9%; UGA specifies at least 5% sodium hypochlorite and no scented products. Shop unscented household bleach on Amazon →
  • A clean 5-gallon bucket, a funnel, a clean garden hose
  • Your well’s depth, water level and casing diameter (from your well records or the driller)
  • Chlorine test strips (optional, for confirming the flush) WaterTestingKits.com: chlorine test strips →

How much bleach?

Use the official tables. Don’t guess.

  • CDC publishes tables of bleach amounts by water depth and casing diameter for drilled and for dug wells, calculated to reach more than 100 mg/L chlorine (CDC tables). For example, CDC lists 1 cup of bleach for 50 feet of water in a 4-inch drilled well, and 2½ cups for 50 feet of water in a 6-inch well.
  • UGA uses 3 pints of bleach per 100 gallons of water in the well, plus 3 extra pints for household plumbing. It gives gallons per foot by casing size: 4-inch = 0.653, 6-inch = 1.47, 8-inch = 2.61 (UGA).

UGA’s worked example: a 6-inch well with 204 feet of water holds 204 × 1.47 = 300 gallons. 300 ÷ 100 × 3 pints = 9 pints, plus 3 pints for plumbing = 12 pints (1.5 gallons). UGA says not to exceed the recommended amount, because extra bleach just means more flushing.

The two methods give different amounts. Use one source’s method consistently, and ask your health department which it prefers.

The process (drilled or driven well), summarized from CDC

  1. Turn off the pump’s power and clear debris from the top of the well. Repair the electrical system and pump if needed; use a professional if you’re not experienced.
  2. Start the pump and run water from the outside faucet nearest the well until it runs clear. That keeps contaminated water out of the house plumbing.
  3. Close valves to any water softener.
  4. Mix the measured bleach with 3–5 gallons of water in a 5-gallon bucket.
  5. Remove the vent cap and pour the mixture into the well with a funnel, avoiding electrical connections.
  6. Connect a clean hose to the nearest outside faucet and run water back into the well to mix it. Rinse the inside of the casing for 5–10 minutes.
  7. Open each indoor faucet until you smell a strong chlorine odor, then turn it off. UGA adds: flush toilets one at a time, and if you can’t smell chlorine at every tap, add more bleach and repeat.
  8. Let the chlorinated water stand in the well and plumbing for at least 12 hours. UGA says 12–24 hours.
  9. Drain the chlorinated water through an outside hose onto an area without plants, such as a driveway, until the chlorine smell is gone. Avoid streams and ponds. UGA also warns against sending more than 100 gallons of chlorinated water into a septic system.
  10. Run the indoor faucets until the chlorine smell is gone.

Dug and bored wells follow a similar process with a different bleach table, and CDC notes they’re harder to disinfect successfully. See CDC’s page for both.

Retesting

  • Until the water has been tested, CDC says to boil it (rolling boil for 1 minute) or use another water source.
  • When: CDC says wait at least 7–10 days, after all chlorine is flushed. Penn State suggests about 10–14 days; UGA suggests 5–7 days with daily water use. Follow your health department’s or lab’s timing.
  • What: total coliform plus E. coli or fecal coliform.
  • Follow-up (CDC): if the result is clean, test again in 2–4 weeks and again in 3–4 months. After that, check bacteria at least twice a year.
  • If bacteria are still present: CDC says repeat the disinfection and retest. If it keeps failing, contact your health department.

Find a lab: EPA certified lab directory, your county health department, or a mail-in kit with overnight cold shipping Tap Score: Advanced well water test →.

If bacteria keep returning, compare continuous disinfection options: Well Water Treatment Options: UV vs RO vs Softener vs Whole-House Filter

Sources

  • CDC, How to Disinfect Wells After an Emergency (May 29, 2025): https://www.cdc.gov/water-emergency/about/how-to-disinfect-wells-after-an-emergency.html
  • UGA Extension, Disinfecting Your Well Water: Shock Chlorination (C858-4, rev. Apr 17, 2026): https://fieldreport.caes.uga.edu/publications/C858-4/disinfecting-your-well-water-shock-chlorination/
  • Penn State Extension, Shock Chlorination of Wells and Springs: https://extension.psu.edu/shock-chlorination-of-wells-and-springs
  • EPA, What to Do With Your Private Well After a Flood: https://www.epa.gov/sites/default/files/2015-05/documents/epa816f05021.pdf

Private Well Water Testing: The Complete Guide for Rural Homeowners (2026)