How to Shock a Well and Treat Bacteria in Well Water
Article Summary
Shocking a well means disinfecting the well and household plumbing with a measured chlorine solution, circulating it, allowing contact time, flushing and then testing the water. It may be appropriate after a contamination event, construction or repairs. If bacteria return, investigate the cause; UV can provide ongoing treatment of water passing through a properly selected and maintained system.
- Follow a complete shocking, flushing and retesting procedure.
- Investigate recurring bacteria rather than repeatedly shocking.
- Size UV and pretreatment to your water test and peak flow.
Updated October 19, 2026 · Practical guidance and product specifications are linked below.
Use a safe alternative water source for drinking, cooking and brushing teeth until your local health department or testing laboratory confirms the water is suitable. After flooding, damaged wiring or suspected fuel or chemical contamination, contact a licensed well contractor and your health department before treatment. Boiling or disinfection will not make chemically contaminated water safe. See CDC well-disinfection guidance.
When should you shock a well?
Shock chlorination may be appropriate after a positive bacteria test, well construction or repairs, or a contamination event such as flooding. Test routinely rather than shocking automatically every year. Follow your local health department's instructions for your well and situation.
Why does my well still test positive after shocking?
Bacteria may remain after incomplete treatment or re-enter through a problem with the well. Ask your laboratory about sampling and your licensed well contractor about the treatment and possible entry points. Have the well cap, casing, drainage and potential contamination sources inspected. Repeated treatment without correcting the entry point can leave the underlying problem unresolved. UGA Extension explains when shock chlorination is appropriate and when recurring contamination needs another approach.
Before you begin: testing, dosing and equipment
- Identify the well: gather its construction record, casing diameter and standing water depth. Total drilled depth alone is not the volume of water to disinfect.
- Use a complete local procedure: ask your health department or well contractor for the correct bleach concentration, dose, contact time and sampling instructions. Do not guess a fixed number of gallons or mix dosing instructions from different protocols.
- Protect equipment: check manufacturer directions for the pressure tank, water heater, softener, UV system, carbon filters and RO equipment. Bypass, isolate or disinfect each as directed; concentrated chlorine can damage some components.
- Plan for downtime: arrange safe alternative water and tell everyone in the household when the plumbing will be unavailable.
How much bleach should I use to shock a well?
There is no single bleach amount that fits every well. The dose depends on the casing diameter, depth of standing water, bleach strength and the complete disinfection procedure being followed. A well’s total drilled depth is not the same as its standing water depth. Have a well contractor confirm unknown measurements.
Use the UGA Extension dose calculation and complete shocking procedure with local guidance. Follow that procedure’s bleach concentration, mixing, contact time, flushing and retesting instructions together; do not combine a dose from one protocol with steps from another.
How to shock a well: the treatment sequence
This overview explains the sequence; use the complete UGA Extension procedure and dosing guidance with local approval. Flooded or damaged wells need professional assessment first. Do not combine its dosing method with another protocol.
- Inspect and prepare. Correct well defects, clear debris and protect treatment equipment. Turn pump power off before accessing the well.
- Calculate the chlorine dose. Use the selected protocol's water-volume calculation and the concentration on the plain, unscented bleach label. Have a contractor establish unknown measurements.
- Add and mix. Add the prepared solution as directed, avoiding electrical connections. Restore pump power only when safe; recirculate through a clean hose and wash down the casing according to the procedure.
- Distribute through the plumbing. Treat the required hot and cold lines and fixtures. Confirm distribution as the protocol directs, then shut the fixtures.
- Allow contact time. Secure the well with power isolated during closure. UGA specifies a 12–24-hour treatment period; do not use household water during that interval.
- Flush carefully. Discharge the highly chlorinated water outdoors to an approved location, protecting waterways, plants and septic systems. Then flush indoor plumbing and restore equipment according to its instructions.
- Retest before drinking. Chlorine odor disappearing is not proof that bacteria are absent. Arrange laboratory sampling after the required waiting and flushing period.
When can I drink the water again after shocking a well?
Contact time, flushing time and laboratory clearance are separate steps. Follow the sampling schedule your local health department or certified lab specifies. CDC's emergency guidance advises waiting at least 7–10 days after disinfection to test, with chlorine thoroughly flushed before sampling. Continue using safe alternative drinking water while awaiting results and follow-up advice.
Test for total coliform and E. coli or fecal coliform as directed. A positive result needs follow-up with your lab and well contractor. For routine care, CDC recommends annual well-water testing for total coliform, nitrate, total dissolved solids and pH. Read CDC's well-testing guidance.
Iron bacteria are a different problem
Rust-colored slime, staining and musty odors may indicate iron bacteria. These organisms are not known to cause disease, but their deposits can clog equipment and create conditions favorable to other organisms. A UV chamber does not remove established slime from the well or plumbing. A licensed well contractor may need to physically clean the system and apply appropriate treatment. Minnesota Department of Health: iron bacteria.
Shock chlorination vs. ongoing UV disinfection
Watch: UV Water Disinfection vs. Chlorine Shock
VIQUA’s video introduces the two approaches. Use the linked public-health procedures above for well-shocking and retesting instructions.
Well shock vs. UV: benefits, upkeep and limitations
| What to compare | Chlorine well shock | UV water disinfection |
|---|---|---|
| What it disinfects | The well and plumbing included in the procedure. | Water flowing through the UV chamber; not the well or existing plumbing biofilm. |
| Ongoing treatment | A treatment event; it does not prevent future contamination. | Continuous treatment while powered, maintained and operated within the system’s water-quality and flow limits. |
| Microorganism reduction | Depends on the chlorine dose, contact time and contamination conditions. | Performance depends on the system, microorganism, water quality, flow and UV dose. Check the exact model’s performance claims. |
| Maintenance and follow-up | Correct dosing, contact time, flushing and laboratory retesting. | Scheduled lamp replacement, sleeve cleaning, filter changes and water testing. |
| Alarms and monitoring | Follow-up laboratory testing confirms the treatment result. | A lamp-failure alarm warns about the lamp. Some models also monitor UV intensity or dose. Continue water testing as advised. |
| Chemical handling | Requires handling chlorine and managing the chlorinated water safely. | The UV stage adds no disinfecting chemicals. Well and plumbing sanitization may still be needed. |
| Taste and odor | Chlorine must be flushed as directed before sampling and returning to use. | UV itself does not change taste or odor, but does not remove existing taste or odor problems. |
| What still needs attention | Well defects and sources of recontamination must be corrected. | Well defects, suitable pretreatment, chemical contaminants and downstream contamination need separate attention. |
UV inactivates susceptible microorganisms using UV-C light. Performance depends on the organism, delivered dose, flow, incoming water and equipment condition. A lamp-on indicator or absence of alarms does not establish microbiological safety. VIQUA explains its testing and performance limitations. UV also provides no continuing disinfectant residual beyond the chamber; see CDC's explanation of treatment and distribution.
What pretreatment does well-water UV need?
Choose pretreatment from a water test and the specific UV manual. Sediment filtration is commonly needed; hardness, iron, manganese, tannins or poor UV transmittance may require additional treatment. A 5-micron filter alone is not a guarantee of suitable water. See VIQUA's pretreatment guidance and our guide to getting reliable UV performance.
UV does not remove chemical contaminants such as nitrate, arsenic or lead. Choose any additional treatment based on laboratory results and the product's specific contaminant claims. Read CDC's comparison of home treatment methods, our sediment-filter guide and carbon-filter guide.
Compare three UV options for well water
UV dose is the amount of UV energy delivered to the water. The same system can treat fewer gallons per minute when a higher dose is required. Compare flow ratings at the dose and water quality your application needs.
Which UV setup should I choose?
- Already have suitable pretreatment? Consider a standalone system such as the VIQUA VH200 if its capacity fits your peak demand.
- Need sediment filtration and UV together? Compare the VH200-F10 and higher-flow VH410-F20. Neither package includes carbon filtration.
- Need additional monitoring? Ask about a system with a UV-intensity sensor or dose monitoring. The three models below have lamp-failure alarms, without UV-intensity sensors. Review certification and performance requirements with your specialist.
These are options to evaluate after testing and correcting well problems. Match measured peak simultaneous demand to the flow rating at the required UV dose. Bathroom count alone is not a sizing method.
VIQUA VH410-F20
For higher peak demand with sediment prefiltration.
18 GPM at 30 mJ/cm²
14 GPM at 40 mJ/cm²
Includes a 5-micron sediment prefilter, lamp countdown and lamp-failure alarm. Carbon filtration and UV-intensity monitoring are not included in this configuration.
View VH410-F20 →
VIQUA VH200-F10
For lower peak demand with sediment prefiltration.
9 GPM at 30 mJ/cm²
7 GPM at 40 mJ/cm²
Includes a 5-micron sediment prefilter, lamp countdown and lamp-failure alarm. Carbon filtration and UV-intensity monitoring are not included in this configuration.
View VH200-F10 →
VIQUA VH200
For a standalone UV stage with suitable separate pretreatment.
9 GPM at 30 mJ/cm²
7 GPM at 40 mJ/cm²
Includes a lamp countdown and lamp-failure alarm. No integrated sediment or carbon filter and no UV-intensity sensor.
View VH200 →Manufacturer specifications: VH410-F20, VH200-F10 and VH200. Ratings depend on the manufacturer's specified conditions. Current prices, availability, manuals and configuration details are on each product page.
Need integrated sediment and carbon filtration, a monitored system or a different capacity? Compare more options in our UV buyer's guide, NSF/ANSI 55 Class A and Class B guide and UV system collection.
Get help sizing your well-water UV system
Share your laboratory water results, measured peak flow and existing filters with ESP Water. We'll help you compare pretreatment, capacity and monitoring options before you buy.
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FAQs
Does Well Water Have Chlorine?
Untreated groundwater usually has no added chlorine. Chlorine may be present after well shocking or where a continuous chlorination system is installed. UV adds no chlorine and treats water only as it passes through the chamber. Learn more about UV treatment for well water.
How Often Should I Shock My Well?
Test your private well at least annually and after events that may affect its water quality. Shock chlorination is appropriate when indicated by test results, repairs or contamination, following local guidance; it is not an automatic annual task. If bacteria return, have a licensed well contractor investigate the cause. See CDC testing guidance and our bacteria-treatment guide.
How Long Does It Take for a Well to Clear up After Disinfecting?
The chlorine contact period is not the same as clearance to drink. Complete the prescribed treatment and flushing, then follow your certified lab or health department’s sampling schedule. CDC emergency guidance advises testing at least 7–10 days after disinfection, after chlorine is thoroughly flushed. Continue using safe alternative drinking water until results and local advice confirm suitability. Water looking clear or losing its chlorine odor is not proof of safety.
How Does Well Water Become Contaminated with Bacteria?
Bacteria can enter through a damaged or poorly sealed cap, cracked casing, construction defects, flooding or contaminated surface water. Septic leakage and animal waste are possible sources. A well contractor can inspect likely entry points. Correct the source, then select any ongoing treatment using a water test. See our well-water UV guide and UV system buyer’s guide.
