How to Shock Chlorinate a Well
To shock well water, you pour a measured dose of plain household bleach down the well, circulate it through every pipe and fixture in the house, let it sit overnight, then flush it out and retest for bacteria. It's a one-day job for most drilled wells with a submersible pump, plus a few days of flushing and a lab test to prove it worked.
Shock chlorination is a one-time cleanup. It kills bacteria that got into the well and plumbing, but if something keeps letting them in, they'll be back.
When to shock a well
UGA Extension lists the times to do it:
- After a new well is finished, or an unused well goes back into service.
- When a test shows bacteria.
- After the system is opened for installation, repair or maintenance, like pulling the pump.
- When floodwater surrounds or covers the casing.
- When the water turns muddy or cloudy after rain.
- When you see signs of iron or sulfur bacteria, like slime or odor.
The Tacoma-Pierce County Health Department's procedure is written for wells that have tested positive for coliform. Either way, test first if you're not sure. Our page on coliform bacteria in well water explains what a positive result means, and well water testing covers how to sample.
Not every well suits a DIY shock. Mississippi State Extension says its procedure is for wells with a working submersible pump, and that it won't work on a well with a jet pump or one that's damaged. Tacoma-Pierce County says hand-dug wells, sand points and springs need other procedures. For those, call your county health department or a well contractor.
Tools and materials
- Plain, unscented household bleach. UGA calls for at least 5% sodium hypochlorite. Skip scented products, and skip "concentrated" or ultra bleach, which Tacoma-Pierce County warns will over-chlorinate.
- A clean 5-gallon bucket and a funnel.
- A garden hose that reaches from an outdoor spigot to the wellhead.
- A wrench or socket for the well cap bolts.
- Goggles, rubber gloves, an apron and boots.
- Bottled water for drinking for a day or two.
Mississippi State says to use bleach less than 6 months old. Bleach loses strength sitting on a shelf, and a weak jug means a weak shock.
How much bleach to shock a well
You need two numbers: the casing diameter and the depth of water standing in the well. Water depth is total well depth minus the static water level. Both are usually on the well log or the driller's report.
UGA's method is 3 pints of bleach per 100 gallons of water in the well, plus 3 more pints for the pressure tank, water heater and pipes. To get the gallons, multiply the water depth by the storage per foot:
| Casing diameter | Gallons per foot of water |
|---|---|
| 4-inch drilled | 0.653 |
| 6-inch drilled | 1.47 |
| 8-inch drilled | 2.61 |
| 24-inch bored | 23.5 |
| 36-inch bored | 52.9 |
Worked example: a 6-inch well with 100 feet of water holds about 147 gallons. That's about 4.4 pints for the well plus 3 pints for the plumbing, so roughly 7.5 pints, a little under a gallon.
Don't add extra "for good measure." UGA says to stay at the recommended amount because excess bleach just means more flushing. State and county tables differ a bit because they assume different bleach strengths, so if your health department publishes one, use theirs.
Steps
Run water first if it's cloudy. Mississippi State says to run a hose from the nearest outdoor faucet until it runs clear.
Bypass treatment gear. Disconnect carbon filters and reverse osmosis units, which chlorine can damage, and check the manual before chlorinating a softener, iron filter or sand filter.
Turn off the pump breaker and remove the well cap or plug.
Mix the bleach into a bucket of clean water and pour it down the well through the funnel, without splashing.
Turn the breaker back on. Run a hose from the nearest outdoor spigot back into the well. UGA says to wash down the inside of the casing for about 15 minutes, until you smell chlorine.
Open every faucet one at a time, outside first, then inside, hot and cold, and shut each one off once you smell chlorine. Flush each toilet. If a fixture never smells of chlorine, UGA says to add 3 more pints to the well and repeat.
Turn off the breaker, put the cap back on, and let the water sit. UGA calls for 12 to 24 hours of contact time. Mississippi State says at least 8 hours or overnight. Start in the evening.
Flush. Run the outdoor spigots first until the chlorine smell is gone, then the indoor taps.
Put filters and softeners back in service, following their manufacturers' instructions for disinfecting them.
Retest. UGA says to wait 5 to 7 days of normal use, then test for total coliform and E. coli. Use a state-certified drinking water lab and follow its sampling instructions.
Don't drink the water until a certified lab says it's clean. Use bottled water or water boiled for 1 minute in the meantime.
Mistakes to avoid
- Dumping all the chlorinated water into the septic tank. UGA says not to send more than 100 gallons of it into a septic system, or into a stream, pond or lake. Run the first flush out a hose onto gravel or a spot where bleached grass won't matter.
- Using too much bleach. Very strong solutions take days to flush and don't disinfect any better.
- Skipping fixtures. Any tap that never smelled of chlorine is a place bacteria can hang on.
- Testing too soon. A sample with chlorine still in it can read clean when the well isn't. Tacoma-Pierce County says not to resample until the taste and smell are gone, and flushing can take two to three days.
- Treating it as a cure. If coliform comes back, something is letting it in. A cracked or loose well cap, a damaged well casing, or surface water pooling at the wellhead are the usual suspects.
When it's a pro job
Call a well contractor or your county health department when the well is hand-dug, a spring or a sand point, when you have a jet pump, when the cap is buried or sealed in a pit, or when the shock didn't clear the bacteria. Mississippi State says a well that fails disinfection may need cleaning before it's shocked again. UGA says recurring contamination calls for finding the source with a licensed driller or adding continuous disinfection.
A well inspection is the logical next step if the bacteria keep coming back.
FAQ
How long should I run my water after shocking my well?
Run it until you can't smell chlorine anymore, outside spigots first, then the indoor taps. Tacoma-Pierce County notes the full flush can take two to three days. Spread it out so you don't overload the septic system or pull the well down.
Can you shower in shocked well water?
Not during the contact period. UGA says no one should use the water for any purpose during the 12 to 24 hours it sits in the pipes. After you've flushed and the smell is gone, bathing is fine for most people, but hold off drinking it until the lab test comes back clean.
Can you flush the toilet after shocking the well?
Yes, you flush each toilet as part of the process so the bleach reaches the tank. During the contact period, keep flushing to a minimum so the chlorinated water stays in the pipes. Afterward, keep in mind the limit of about 100 gallons of chlorinated water into a septic system.
How much does it cost to shock a water well?
Done yourself, it's the cost of a gallon or two of plain bleach and a lab test. A well contractor charges for the visit, and HomeAdvisor puts a typical minimum house call at $100 to $150. Lab fees vary by state.
How do you shock a cistern or a dug well?
Those need different math and often a different method. UGA says to contact your local Extension office for cisterns and other diameters, and Tacoma-Pierce County says hand-dug wells need other procedures. Your county health department is the best first call.
Sources
- University of Georgia Cooperative ExtensionDisinfecting Your Well Water: Shock Chlorination (Circular 858-4) (opens in a new tab)
- Ohio State University ExtensionShock Chlorination of Wells (AEX-318) (opens in a new tab)
- Mississippi State University ExtensionDisinfecting a Water Well Through Shock Chlorination (P3398) (opens in a new tab)
- Tacoma-Pierce County Health DepartmentShock Chlorinate Your Well (opens in a new tab)
- HomeAdvisorHow Much Does Well Pump Repair Cost? (opens in a new tab)