Questions & answers on how to shock or disinfect a drinking water well:

These questions & answers on well shocking, disinfection, or chlorination will help troubleshoot the procedure for building owners or service providers who need to disinfect a water well.

This article series 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.

Page top sketch illustrating both deep and shallow water well construction and depths is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Questions & Answers on How to Shock or Chlorinate a Well

Questions & answers on how to sanitize a well, posted originally at WELL CHLORINATION & DISINFECTION - be sure to see the procedures and advice given there.

Question: warning that bleach may not mix in very deep wells with a large static head

8/13/14 Mark said:

I followed this guide over the weekend and thought I'd share a comment on something that happened during the procedure that I didn't see mentioned here or was simply an anomaly with my well.

I introduced the bleach around noon on Saturday, followed by a generous amount of water from my hose as advised.

However, I did not detect the odor of bleach until Tuesday. I don't know the weight of bleach versus water but it certainty took some time to get to the pump or tank itself. Is this normal? Is it due to the depth of my well (520ft. shaft depth, 300ft. of water I think)?

Reply: specific gravity of household bleach

Mark,

Thanks for the helpful comment; we'll keep it for future readers.

Indeed in a very deep well it could take some time for bleach to properly mix in the water inside the casing, especially if the well is deep - and even longer if the mistake is made of dumping in solid chlorine tablets.

A recommended procedure that works if you can get a hose from building water supply back to the well is to recycle water using a garden hose, washing down the casing sides and thus avoiding running out the well while mixing in the bleach. Without adequate bleach concentration and exposure time the well shock procedure may not be effective.

The specific gravity of household bleach by the research I found is typically around 1.16 - where the specific gravity of water is 1 (ignoring temperature variations). So bleach should sink slowly through water, all else being equal.

Question: cost to shock a well?

(Aug 14, 2014) Eric said:
Generally, how much does professionals charge for shocking a well with coliform?

Someone charged me $420, am I robbed? thanks

Reply:

Eric,
$420. would be steep for simply opening an accessible well casing and pouring a proper dose of bleach into a well. But if you add work to find, uncover, open difficult connectors, calculate or determine well depth and static head water volume, thus calculate the proper bleach dose,

then flush and wash down casing sides, possibly returning to flush the bleach out of the system 24 hours later, the amount would not be at all excessive at North American prices. In short, it depends on what work was done.

Question: long wait to flush out chlorine

(Aug 22, 2014) Anonymous said:
I am planning to go out of town for a week. If I shock the well before I leave is that time frame too much until I return home to flush it out?

Reply:

Good question:

If you shock to the recommended concentrations you're probably ok - what I'm thinking about (worried) is the mistake of leaving high concentration bleach in contact with any rubber or plastic components too long.

Chlorine is quite volatile and tends to leave water in which it's dissolved, but in an enclosed system its effects may remain for a longer time than one would think.

Question: remove wiring before shocking the well?

(Sept 29, 2014) Anonymous said:
Shouldn't the wiring that is packed into the top be removed before pouring in the clorox mixture?

Reply:

I agree that we do not want to wet electrical components. The splices are normally at the top of a well into which electrical wires run; lower in the well they must be waterproof; wash down the well sides and interior during the process.

Question: well close to the Winnipeg River

(Oct 6, 2014) Ted said:
I have a dug well close to the Winnipeg river ( distance to water's edge is from 20 ft. to 0 ft., when the river is high and the top of the well is underwater).

It is in a vertical black plastic culvert, 4 ft. in diameter and approximately 10 feet deep. As the actual volume of water in the well varies, I need to know what would be the safe ratio of chlorine to well water to shock the well which was submerged for much of the summer.

I can measure the current water depth, as the well has a removable screw-on plastic cap. I also have a Triplex UV water treatment system on the water line between the in-home pump/pressure tank and the house water supply. I intend to replace the filters during this process. What would be the best point in time to do that?

Reply:

Ted,

A well that is flooded is at extra risk of contamination from anything in the floodwaters: sewage, chemicals, salts, etc.

WELL CHLORINATION & DISINFECTION answers your question of how much bleach to use to sanitize the well - but that will NOT address any chemical contaminants that may be entering the water system. I would not consume water from such a flooded well before having the water tested to determine if other water sanitation and treatment steps are needed to provide safe drinking water.

UV treatment addresses bacteria, not other contaminants.

After shocking the well and flushing the piping system you'd replace filters.

Question: murky water after chlorination

(Mar 7, 2015) bob said:
Sisters well treated cholerine- smell in house, water murky. How long should it take to clear up. When safe to drink

Reply:

Bob, shocking the well does not address suspended solids or murkiness. I'd have the water tested to see what's going on.

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.

Reader comments:

(June 9, 2015) Anonymous said:
I have read several articles on INSPECTAPEDIA (wells, pumps and water pressure) and have found them to be most helpful.

The articles are detailed thorough and well written but most significantly they are easy to understand. A great find and a more reliable source of information than many U TUBE sites.

Reply:

Thank you Anon: we're gratified that you found InspectApedia useful - we work hard to provide accurate, researched information and to that end we also welcome questions, critique, or content suggestions. - Ed.

Question: thick orange water after shocking well

(July 21, 2015) John said:
I just shocked my 400ft deep well with a litre of bleach and thick orange water came out in the toilet for 3 days. It was enough to clogg the filters so I bypassed them. The water is slowly getting clearer. Could this be rust. There is very low iron content on my water before.

Reply:

I agree that sounds odd. Could the shocking procedure have distrubed rust on the casing interior or on or in building piping or water tanks? Or was so much water run to flush out the bleach that we ran the water level so low in the well that we picked up debris and silt?

Also: the 400 ft depth is not the important number - what's important is the actual volume of water in the well - the static head. That's how you determine the proper amount of bleach to use.

Question: trouble getting rid of bleach in the well

(Oct 5, 2015) wendyk said:
We shocked our 400 ft well 10 days ago, following the exact procedure. We have been flushing the well every day, all day outside of the house, turning it off at night.

We test it every day with a high quality water testing kit. The bleach content is still high, and is not clearing, and the odor is still very strong. Any suggestions?

Reply:

Wendy:

If you used liquid bleach at proper concentration then it should flush out of the well; if you used solid bleach tablets the flush out can be much more difficult - very difficult, though steps to speed tablet dissolution such as injecting a hose into the well bottom to try to speed the process might help.

Try washing down the well casing sides by circulating water through a garden hose to the well casing;

Also you can calculate the volume of water that's in the well casing; running out that volume of water as well as water in the well piping and building water tank and pipes should significantly reduce the remaining bleach level.

It won't immediately remove all bleach as the flow rate of water into the well is a factor; a low flow rate well means that the dilution of bleach-containing water in the well is slowed.

Finally, try turning off the pump and draining your water tank, and turning off your water heater and draining that tank completely; then re-fill the tanks and start anew.

Reader follow-up:

Thank you for your reply. I'm sorry, but I forgot to say it is 780 foot well with a static water level of 400 feet. Yes, we have done everything you suggested. We used 1/4 cup of fast disolving powder and also liquid bleach as recommended for such a deep well. I guess we will continue flushing.

Question: used bleach tablets to disinfect the well, now trouble getting rid of the bleach

(Nov 10, 2015) George said:

We had our submersible pump pulled and replaced three weeks ago. After replacing the pump, the well service man added a cap full of tablets down the well to disinfect it. He didn't really measure or count the number of tablets, in fact there was a few extra tablets in the bottle, so through them in there also.

Needless to say he way over treated the well. This was three weeks ago and we still have chlorine smell and taste in our water.

I have flushed it outside for hours at different times, as well as in the house. The well man has came back out to house and he thinks some of the tablets may be have not completely dissolved, or the concentrate of the of the chlorine is still on the bottom of the well.

Our well is a strong producing well, at least 20 gallons a minute and the pump is sitting 30 feet off the bottom off the well. Today when he came back out he said he wants me to keep running it and hopefully it will clear up.

The next step may be to have the well air blasted, but I am reluctant to do this. I'm thinking maybe we should lower the pump to approximately 5 foot off the bottom of the well and then let it run. I am open to any suggestions as I really don't want to air blast the well if at all possible.

Reply:

Try recirculating water thru the well using a garden hose, leave it running 24 hrs or more to try to spreed up dissolution of the tablets. Monitor chlorine level. If it goes up this approach may be working.

Then flush the well.

Keep me posted.

Question: foamy water after shocking / chlorinating the well

(Nov 13, 2015) tracy said:
Every time we chlorinate our well, upon running out the treated water we get foamy water, for days.

Fill a sink, get inches of foam that looks just like soap suds.

Turn off water, you can hear the fizz of bubbles popping, but still lots of small bubbles on surface even after 10 minutes.

Running an outside faucet into a bucket, foam built up like something alive , cascaded over side of bucket onto ground and held its shape till water turned off. What is this?

Reply:

I don't know, though detergents can cause foaming; most-likely but you are describing a chemical reaction, perhaps between lime deposits - hard water - and an acid, perhaps formed as you treat the water.

Try having the water tested for hardness, minerals, pH

Question: effect of chlorine on the pumping machine inside the well during chlorination

2016/03/17 Rotimi Jacobs said:
what is the effect of chlorine on the pumping machine inside the well during chlorination

Reply:

Rotimi

At the recommended concentrations of disinfectant when shocking a well, I've not read of damage to the water pump from the chlorine.

Question: trouble using lemon-scented bleach to shock or chlorinate a well?

Linda said:
What happens if you use lemon scented bleach? I did not realize that I should only use non-scented.

Reply:

I don't know, Linda but I suspect you'll have a bit of extra purging to get rid of both bleach and lemon scent in your water.

"Some chlorine may persist in the system for 7–10 days. Water with a slight chlorine smell should be usable for most purposes. If the odor or taste is objectionable, simply let the water run until the chlorine dissipates." - Wright (1997)

If the scent is gone and your water test finds no remaining bleach, my OPINION is there is probably no measurable-hazard remaining.

Scented products can be a particular hazard for asthamtics, people with multiple chemical sensitivity, and similar conditions. The example MSDS sheets we retrieved for lemon bleach or lemon-scented bleach describe the product in overview as not hazardous but do give various precautions, some of which we excerpt below. Keep in mind that the MSDS documents refer to the bleach product itself, not its properties when it has been dissolved in well water.

References on Using Lemon Scented Bleach when Chlorinating a Well: Lemon-Scented Bleach Hazards?

• Ingber, Arieh, Bente Gammelgaard, and Michael David. "Detergents and bleaches are sources of chromium contact dermatitis in Israel." Contact Dermatitis 38, no. 2 (1998): 101-104.
• MSDS for Clorox Lemon Scented Bleach, [PDF] (2012) retrieved 2016/03/21, The Clorox Company 1212 Broadway Oakland, CA 94612 Tel. (510) 271-7000, original source: http://www.allfloridapaper.com/wp-content/
  uploads/222072-Clorox-Lemon-Fresh-Bleach1.pdf
  Excerpt:
  Eye irritant. May cause skin irritation. May be harmful if swallowed.
  No medical conditions are known to be aggravated by exposure to this product.
• MSDS for Clorox Lemon Scented Bleach, [PDF] - Australia, retrieved 2016/03/21, original source: http://www.msdsonline.com.au/msds/msdsview.asp?Std=1&ID=c8bfa350-7b8f-460e-a0b4-674a5bccaf1a
  Excerpts:
  
  Ingestion: Immediately rinse mouth with water. Do NOT induce vomiting. Slowly give water to drink. Seek medical assistance.
  
  Inhalation: Inhalation of chlorine gas at 1 ppm will irritate the mouth, nose and throat. Above 1.3 ppm, vapours may cause coughing and difficulty breathing.
  
  Risk of delayed onset of pulmonary oedema (fluid in the lungs).
  
  Regulatory information: Not Classified as Hazardous according to criteria of National Occupational Health & Safety Commission, Australia (NOHSC).
  Not classified as a Scheduled Poison according to the Standard for the Uniform Scheduling of Medicines and Poisons (SUSMP).
• Robertson, Jack. "Building brand equity at the Clorox company." Planning Review 20, no. 5 (1992): 59-61. - discusses the addition of Lemon Scent to bleach
• Wright, Marsha, "Disinfecting a Domestic Well with Shock Chlorination", [PDF] Cooperative Extension Service, College of Agriculture & Home Economics, New Mexico State University, Las Cruces NM, 1997 retrieved 2016/03/21, original source: www.aces.nmsu.edu/pubs/_m/M115.pdf - advises against using lemon scented bleach but does not say why.

Question: over-chlorinated the well

(Oct 27, 2014) Anonymous said:
Help. I may have overchlorinated my well.

Reply:

The chlorine will flush out of the well, but if you overdosed with the wrong material, such as chlorine tablets, indeed that will take some time. If the well is too deep to retrieve the solid tablets (if that's what you did) then recycling water through the well can speed the dissolution, followed by a flushout.

...

Continue reading at WELL CHLORINATION & DISINFECTION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see WELL DISINFECTION FAQs-2 - more-recent questions and answers about solving problems when or after shocking a well

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

Or see these

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• WELL DISINFECTION PROCEDURE, POST FLOODING

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