Well depths and types (C) Carson Dunlop AssociatesWell Chlorination Procedure
when and how to shock a drinking water well

  • WELL CHLORINATION & DISINFECTION - CONTENTS: How to shock the well - well shocking procedure. When to shock or chlorinate a drinking water well & What is the procedure to shock or chlorinate a well? How much bleach or hypochlorite do you use to shock a well? When should well water be re-tested after shocking the well? Well shocking details for water filters & Well shocking details for water softeners. Chlorinating water - details for wat
  • POST a QUESTION or READ FAQs about well shocking or well sterilization procedures: how to deal with bacterial contamination in drinking water wells

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

How to shock or disinfect a well: this article explains how to shock a well, when, why, and exactly how to chlorinate a drinking water well. We provide a table explaining the quantity of bleach needed to disinfect a well, and a table comparing the 3 Common Well Water Disinfectants: Chloramine, Chlorine and Chlorine Dioxide.

We include a detailed description of the well shocking procedure using household bleach to sterilize well water and water equipment. The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time. Page top sketch illustrating both deep and shallow water well construction and depths is provided courtesy of Carson Dunlop Associates.

Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.

When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination in Well Water

Unsanitary well opened by owner, needs to be shocked and sealed (C) Daniel FriedmanThis article includes adapted information from the New York Dutchess County Health Department's environmental laboratory, along with other expert sources and with annotations, expansion & annotation. You will find this well shock procedure advice consistent with the well shocking or well chlorination procedures recommended by most health authorities.

[Click to enlarge any image]

Article Series Contents

The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time.

Our photo shows an owner who has lifted the loose, poorly-sealed well piping and cap right off of the steel well casing. This well needed repairs and it needed to be sterilized using the well chlorination procedure we discuss here.

Therefore it is vital that the well be constructed so that no new contamination may enter the well following completion of the shock disinfection. In order to achieve a satisfactory disinfection of the system, the bacteria must be brought in contact with a chlorine solution of sufficient strength and remain in contact with that solution for a sufficient time to achieve a complete kill of all bacteria and other microorganisms.

Details of the Well Chlorination Procedure - Exactly How to Shock a Well, Where to Put Chlorine, How Much Chlorine to Use to Shock the Well

Standard well casing (C) Daniel FriedmanIf drinking water has been tested and has not passed standards for safe drinking, or any time the building water supply system has been opened for repairs (such as replacing a submersible well pump or a jet pump foot valve), the well should be disinfected following these procedures, and should be re-tested as described below.

Our photo shows a standard modern 6" steel well casing - it's easy to spot at a property.

If you don't know where the well is located you'll have to find it before this well chlorination procedure can be best performed.

See WELLS CISTERNS & SPRINGS for articles that describe different types of water wells, what they look like, where they're found, and their operating characteristics.

It's possible to get chlorine into the well by sending it through the building piping and pump but that step won't sterilize the interior and sides of the well casing - so the procedure below is a better one.

  • Pour Clorox™ Bleach (or an equivalent brand of household bleach) or hypochlorite granules down into the well. Some people use swimming pool chlorine tablets which have the advantage that they sink to and sterilize water at the well bottom, and the disadvantage that it takes longer to flush out the chlorine.

    Watch out: also see CHLORINE SAFETY WARNINGS.
  • How much bleach to use when shocking a well: Health department officials can give more precise guidance about the amount of disinfectant needed based on the depth of the well. Common well shocking guidelines for the amount of household bleach needed are given in the table just below. For a separate well disinfection quantity table for difficult cases such as well & equipment disinfection after area flooding see WELL DISINFECTANT TABLE, POST FLOODING.

Quantity of Chlorine or Household Bleach Needed to Shock a Well

Well Depth in Feet (6-inch diameter well casing) Volume of standard household bleach needed
Well depth 100' 3 cups Clorox or 2 oz. of granules.
Well depth 200' 6 cups Clorox or 4 oz. of granules
Well depth 300' 9 cups Clorox or 6 oz. of granules
Well depth 400' 12 cups Clorox or 9 oz. of granules
Well depth 500' 1 gallon Clorox or 12 oz. of granules.

NOTE to be accurate in reaching the necessary concentration of chlorine in your well, treat the "depths" listed above as if they were the height of the actual column of water in your well (assuming a standard casing which is 1.5 gallons per foot of height). So if your well is 400 feet deep, but if 100 feet of it is air, your water depth is actually 300 ft.

Choices of well disinfectants are detailed at WELL DISINFECTANT CHOICES

More about how to measure the actual depth of a well is at DEPTH of a WELL, HOW TO MEASURE.

Watch out: for inadequate well disinfection: use enough bleach to reach the necessary concentration in the well and let the disinfectant remain in the well long enough (8-24 hours) - otherwise you may fail to adequately disinfect the well.

Watch out: for excessive well disinfection: don't significantly "overdose" the well with bleach or chlorine or you may find that you have to waste a lot of water and time flushing out the chlorine bleach at the end of the disinfection period.

Watch out: for difficult-to-sanitize wells or if the water well has been contaminated by area flooding extra steps and extra safety precautions needed. Details are at WELL DISINFECTION after a FLOOD

  • Prepare the well, plumbing system, equipment: fix any leaks, inoperative controls, or obvious nearby contaminant sources. Take any charcoal-filter type water treatment equipment offline.
  • Introduce the chlorine solution into the top of the well. Remove the cap at the upper terminal of the well casing and pour the chlorine solution down the inside of the casing.

    If the well casing terminates through the floor of a pump house, then the casing is required to have a well seal at the upper terminal [i.e. at the top of the casing]. This well seal can be loosened and the chlorine solution introduced into the well at that point. In a large diameter well [such as a public supply company's well], the chlorine solution should be poured or splashed around the wall of the well so that all inside surfaces of the well are brought into contact with the strong chlorine solution..
  • Using a garden hose, spray water down into the well pipe to wash the chlorine solution down to the bottom of the well. Ten gallons of water should be enough. [Running more chlorinated water down the casing sides won't hurt nor risk running the well dry since you're recycling the well water through the plumbing and back to the well.]

    This step in the well shock procedure, by recycling chlorinated water out of the building plumbing and back into the well both cleans the well casing, piping, wiring, and also avoids wasting water.

    Watch out: shock hazard: if on opening the well casing you see exposed electrical wires or flimsy electrical connections you should have a qualified electrician or repair person make sound, water-tight splices and coverings before attempting to wash down the well casing interior.

    Watch out: disinfecting or shocking a well may also be ineffective if the well casing and sides are coated with mineral deposits or biofilm that form in some water wells. Mechanical cleaning may be necessary to obtain a successful outcome. More aggressive water well disinfection procedures are described at WELL DISINFECTION after a FLOOD
  • Turn on all cold water household taps until you can smell the Clorox coming out of every plumbing fixture water supply, including the faucet farthest from the well.

    Watch out: notice that we did not include the water heater system and hot water tank in this step. However you may wish to also turn off and then drain the water heater to eliminate any possibly contaminated water from that tank before restoring your water system to operation. If you elect to shock (sterilize) the water heater tank interior we recommend that that step be performed with the water heater turned off (don't heat a water-bleach mix) and that the heater be left OFF until the tank has been drained and flushed and then re-filled.

    Watch out: Also heating water that contains a high level of chlorine might produce potentially dangerous chlorine gas coming out of a hot water faucet.
  • Turn off the water and do not use it for 8 to 24 hours. Seal the top of the well. Do not run laundry with this chlorinated water or it may bleach clothing unexpectedly. [The BC ME recommends 6-12 hours or longer if possible - Ed.]
  • Flush out the Clorox™ (or other brand) bleach solution: at the end of the standing period, operate the well pump (run the water) water until you can no longer smell the Clorox.

    Watch out: Do not run Clorox™ into the septic system - run water outside through an outside faucet or hose. There should be a hose connection at the at the bottom of the water pressure tank.

    When you no longer smell chlorine at the hose draining the water pressure tank, close off the drain and open all faucets in the house to flush out house piping for fifteen minutes or until you no longer smell or taste chlorine [whichever is longer].

    Watch out: if you do not first drain the water pressure tank of chlorinated water it can take a much longer time to flush the bleach smell out of the water supply. And if you have put chlorinated water into the water heater tank, that tank too will best be flushed out. (Be sure the water heater is turned OFF before draining the heater tank or you can damage that system.

    Watch out: if you forget to take any charcoal-filter equipment offline before introducing a disinfectant you may find it almost impossible to get the bleach odor out of the system later. You may have to replace activated charcoal or charcoal filters in your water treatment equipment if chlorine or bleach odor remains a problem. You will want to replace such equipment in any event if it was contaminated by floodwaters or other sources. Details are at WATER TREATMENT EQUIPMENT DISINFECTION.

    Watch out: If your well has a limited flow rate or poor recovery rate there is a risk that you may simply run out of water during the flush-out step.

    Watch out: if you used a low-odor or "odorless" bleach product to shock the well you may have trouble knowing if you've flushed out all of the bleach product. Leaving bleach in drinking water can be dangerous and of course it could cause some surprises in the laundry too.

    We recommend using chlorine test strips to check for residual chlorine after flushing bleach out of a well water system. - thanks to reader Mike O'Brien for this note, 5/13/2011. Details are at CHLORINE in WATER, HOW TO TEST FOR and at CHLORINE SOURCES in WATER
  • Retest the well water after all the Clorox or chlorine is out of the system and the water has been used for 5-7 days (typical health department guideline) or 7-10 days (my suggestion) after the disinfection.

    The longer you wait until the well water retest the more valid will be the results, because you are giving time for a remaining bacterial contaminating colony to reproduce. We elaborate on this point at "When to re-test your well water" below.

Chlorine & Hydrogen sulfide (H2S) Safety Warnings for Water Treatment Equipment & Well Disinfection

Watch out: when working with chlorine, people should be in a well-ventilated place. The powder or strong liquid should not come in contact with skin or clothing. Solutions are best handled in wood or crockery containers because metals are corroded by strong chlorine solutions.

Watch out: if using chlorine disinfectants in equipment that heats water such water heaters, be sure your heater has been turned OFF and has cooled down to at least room temperature before trying to run chlorine through it. Heating water that contains a high level of chlorine might produce potentially dangerous chlorine gas coming out of a hot water faucet.

Watch out: Leaving too much chlorine in any water system can be dangerous: drinking concentrated chlorinated water could be sickening or even fatal, and less seriously, doing laundry with chlorinated water may bleach clothing by accident.

Watch out: for difficult well or equipment sterilization cases such as after area flooding or where there is a persistent bacteria source, pH adjustment of the disinfection solution may be necessary for the disinfectant to be effective, (WELL DISINFECTANT pH ADJUSTMENT )

Watch out: if the well source water contains hydrogen sulfide (H2S), when preparing a well disinfection solution you must allow the water to aerate so the H2S dissipates, otherwise the acid formed will cause an immediate release of H2S gas from the water, which poses a serious health risk.

For details about exposure to various toxic and irritating gases see

Common Well Water Disinfectants: Chloramine, Chlorine and Chlorine Dioxide

This topic has moved to a separate article found at WELL DISINFECTANT CHOICES.

Well Chlorination Procedure for Water Filters, Water Softeners, and Water Heaters


Well Cleaning & Well Disinfection Procedures after Area Flooding

This topic has been moved to a separate article found at WELL DISINFECTANT TABLE, POST FLOODING

Article series contents

This article series on well water contamination, testing, & cures explains many common water contamination tests for bacteria and other contaminants in water samples. We describe what to do about contaminated water, listing common corrective measures when water test results are unsatisfactory.

We include water testing and water correction measures warnings for home owners and especially for home buyers when certain conditions are encountered, with advice about what to do when these circumstances are encountered. Various treatment methods for contaminated water are reviewed and the pros and cons of each are discussed.




Continue reading at WELL DISINFECTANT pH ADJUSTMENT or select a topic from the More Reading links shown below.


Or see WELL CLEANING PROCEDURES to address clogged well screens, blocked foot valves, or debris in the well bore.

Suggested citation for this web page

WELL CHLORINATION & DISINFECTION at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References