Well depths and types (C) Carson Dunlop AssociatesChlorine Solution Ph Adjustment for Disinfection
How & why to check & adjust the pH of disinfectant solutions for wells & water treatment equipment

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Chlorine solution pH test & adjustment when treating drinking water:

Making sure that a chlorine disinfectant solution used to shock a water well or to disinfect building water piping or water treatment equipment can help determine a successful outcome. This article defines pH - the acidity or basic or neutral property of a liquid, and explains how to test and adjust the pH of a solution as needed when disinfecting a water supply system.

Well disinfection, shocking, & restoration procedures recommended by the BC Canada Ministry of Health & other expert sources include helpful details that can increase the chances that the disinfection is successful, producing potable water.

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Importance of adjusting the pH of Well Water & Well disinfectant Solution

Many experts have discussed the effect of solution pH on the effectiveness of disinfection, including the disinfection of wells and water treatment equipment. Dailloux (1999) for example, points out that certain nontuberculous mycobacteria include resistant strains that tolerate low pH and high temperatures, while other sources point out that high pH is an equally serious concern. (Yu-sen 2002).

And as we cite below, health professionals writing about optimum well disinfection procedures have elaborated the importance checking and adjusting the pH of water and disinfectant solutions.

Explanation of pH levels: the pH (power of hydrogen) of any liquid solution is a measure of how acidic or how basic the solution is. Low pH = acidic. High pH = basic. Solutions with a pH over 7 are considered basic or alkaline while solutions with a pH under 7 are considered acidic. A solution with a pH close to 7 is essentially neutral.

Lemon juice or vinegar and some soft drinks such as Coke® are common household acids; ammonia (NH3) is a common weak base while household bleach is very alkaline - a strong base.

What this means to a non-scientist is that when attempting to disinfect a well or water treatment equipment, taking the time to check and if necessary adjust the pH of a solution can make the difference between a successful disinfection and a failure. Essentially we want a neutral pH or a pH in the range of 6-7 by some sources or pH of 7-7 by others (Hua 2002).

Reader Mark has encountered and discussed the importance of pH (and also well casing deposits) when chlorinating a water well. Mark posted as a comments on 3/22/2013 & 1/31/2014

Bacteria can hide behind surface rust/debris on well casings. Taking two different samples, one from the casing and one from the aquifer should identify this situation: google this procedure; basically for casing samples you figure how much time it takes to pump the water in your discharge pipe out and add a minute to it, pump and take sample; for the aquifer sample you have to do the same basic procedure, but with figuring the amount of water in the well casing (no problem running well beyond such time, assuming that you're not risking running dry).

I've got a 35' well (been out of use for a good ten years, no real history, was left open) that I'll be rehabbing shortly. One of the things that I'll be doing is running a casing brush (WireHog) to clean the casing. I'll also be blowing out the well casing to make sure that there's not a bunch of crud in there.

Upon completion of this cleaning I will shock by back-flushing about 500 gallons of "treatment" (sodium hypochlorite and water) based on the optimal mixture ratio.

Watch out: if you use too strong a disinfectant solution you may not kill the bacteria: you end up increasing the pH level and defeating the biocidal capacity of the sodium hypochlorite, not to mention potential damage from increased pH levels on the casing, pumps and screens: test the pH and adjust with vinegar

I was ignorant of all of this and just dumped a gallon of bleach down the well. Clearly this didn't rectify my problem (and I now know why this might be so). The Alberta Agriculture and Rural Development has an excellent online page on Shock Chlorination [citation given in this article - Ed.].

Mark continued on 1/31/2014

Actually, one of the best places for bacteria to live is in the static to draw-down area.

I should have also stated that slime-forming bacteria can hide the real nasty stuff (coliform and e-coli). And the slime can inhabit all down the casing, the screens and out in to the aquifer. According to Well folks it can be necessary to brush out a well in order to achieve a good kill on the bacteria.

Again, pH IS EXTREMELY IMPORTANT! [The writer's reference citation from the Canadian BC Ministry of Environments given at the end of this section]

In general, they adjust water in a tank to a pH of 4.5 and THEN add chlorine. I wasn't aware of this procedure until after I mixed up my solution. Now that I have an actual personal experience in this I think that I can comment on it... I mixed up a 200ppm sodium hypochlorite solution (8.25% Clorox) in 275 gallons of pH neutral water (my spring water is nearly dead-on, 6.8 - 7.0 pH). I had ASSUMED, based on all the casual experts comments (in addition to information from various water publications [people that actually should be responsible]), that I shouldn't be too far off pH-wise- WRONG! I'm over 8.4 pH!

If you read the [BC health ministry document cited & linked below] you'll find that having a pH value that is much beyond neutral won't be effective as a biocidal. All of this should tell folks why they have difficulties really getting the job done and then have to end up shelling out a lot of money to pay a professional.

I am now trying to adjust the pH down... (don't have a lot of time before I lose the chlorine efficacy). Yes, there is a reason why the good professional well folks should earn what they do.


Re: Mark's 2013 comment

Excellent points Mark - which explains why it can be difficult to sanitize a well, but ONLY if there is actual exfoliating rust inside the well casing - which is not usually the case. Normal surface rust is not a substantive block to disinfectants used in a well. But a thick mineral deposit that may build up in some wells (in the area of the casing or well borehole that is normally water-filled) can make disinfection more difficult in those wells unless disinfection is accompanied by mechanical cleaning.

We agree that what is important is using a proper strength of disinfectant, for an adequate time, followed by through flushing of the well and after a suitable wait time, a follow-up test.

The well sanitizing procedures we document at InspectApedia cite U.S. & Canadian federal and state expert sources & health departments - those are the most expert people we can find.

Mark's 2014 comment was in regards to mine:

"it can be difficult to sanitize a well, but ONLY if there is actual exfoliating rust inside the well casing - which is not usually the case. Normal surface rust is not a substantive block to disinfectants used in a well."

We agree completely.Just below for reader convenience and also at References [5] we have cited and link to a PDF file copy of the helpful BC ministry document to which Mark refers. My original comment was directed at typical residential well disinfection and
the PROCEDURE & QUANTITY of BLEACH NEEDED to SHOCK A WELL - and did not adequately focus on on pH adjustment and on disinfecting a well contaminated by area flooding - a more extreme situation that may have forced floodwaters into the aquifer itself.

For a detailed procedure for disinfecting a well after area flooding see this helpful document cited both in our references and again just below:

"When Standard Water Well Chlorination Procedures are Ineffective: fact Sheet developed for Well Drillers, Health Authority Staff and others involved in well recovery efforts after a flood " [PDF] - British Columbia Ministry of Environment, retrieved 1/31/2014, original source: http://www.env.gov.bc.ca/wsd/ plan_protect_sustain/groundwater/ wells/factsheets/PFRA_well_recovery.pdf

In addition to the pH problem in disinfecting flooded wells, I add Manci's caution about giardia:

Chlorine kills bacteria, including disease-causing organisms and the nuisance organism, iron bacteria. However, low levels of chlorine, normally used to disinfect water, are not an effective treatment for giardia cysts. A chlorine level of over 10 mg/1 must be maintained for at least 30 minutes to kill giardia cysts. -- References [3]

The document from the BC ministry makes a sound point that it can be difficult to disinfect a water well following a flood, giving two reasons why well disinfection may be unsuccessful.

  1. The groundwater may still be contaminated with flood water or there may be a source of continuing contamination.
  2. The well was infrequently (or never) cleaned prior to the flood, and over time large quantities of mineral scale and biofilm have accumulated in the well. This material can greatly impair attempts to disinfect a well.

pH Test Kits - litmus paper in rolls or strips read water or disinfectant solution pH level

Hydrion pH test strips from MicroEssentialsLab

Simple litmus paper (made from paper and dyes extracted from lichens) test strips can be used to test water for its pH level: acids turn litmus paper pink while bases turn litmus paper blue.

You can purchase pH test kits and strips at drug stores, swimming pool suppliers, test equipment suppliers, some plumbing suppliers, and of course, online.

  • Hydrion pH test strips, include a simple color scale that gives pH readings between 0 (acidic) and 13 (basic) - www.microessentialslab.com
  • pHion Balance Diagnostic pH Test Strips, produced by pHion balance
  • pH-Strips, Enzymedica

How to Adjust Water & Disinfectant pH when Shocking a Well

Adapted from "When Standard Water Well Chlorination Procedures are Ineffective:... " - British Columbia Ministry of Environment, retrieved 1/31/2014, original source: http://www.env.gov.bc.ca/wsd/ plan_protect_sustain/groundwater/ wells/factsheets/PFRA_well_recovery.pdf

Fresh potable water in the mixing tank to be used for preparing the disinfectant solution to be injected into the water well should be tested for pH level.

The target pH for fresh potable water intended for disinfection is 4.5 (before adding chlorine) - this is equivalent to a weak acid solution.

Before adding the chlorine solution, you can lower the pH of water by adding a safe weak acid such as household vinegar (acetic acid). Depending on the observed pH you may need to add 20 as much as Liters of 5% acetic acid (household vinegar) to 1000 Liters of water. Slowly add the acetic acid to the water while stirring the tank and then check the pH again as needed until you've reached the target pH.

Watch out: the pH of the water supply plays an important role in the corrosion of copper and brass piping and plumbing fittings or parts.

How to Add the Chlorine (household bleach, sodium hypochlorite) to the Water to Prepare Well Disinfectant

When the water is at the proper pH, add the required amount of chlorine -
see WELL DISINFECTANT TABLE, POST FLOODING for the quantity of bleach you will need.

Lower the pH of the water in the mixing tank to a pH of 4.5 before adding the chlorine; a weak acid like vinegar (i.e. 5% acetic acid) can be used for small well applications since it is readily available and fairly safe to use (20 L of 5% acetic acid may be required for every 1000 L of water added to the well).

Watch out: the Canadian Ministry of Environment warns in the source document that because we are adding chlorine to a weak acid (pH 4.5) some chlorine gas will form. Chlorine gas can be harmful or even fatal at high concentrations and exposures. The ministry recommends:

To lower the pH in the mixing tank, slowly add the acid to the water while checking the pH level with pH test strips. Agitate the water to ensure uniform distribution of the acid.

Always prepare the chlorine solution outside in a well-ventilated area and stand up-wind when adding the chlorine to the acid solution.

Watch out for hydrogen sulfide (H2S - which produces a rotten egg or sulphur smell) in the water. This gas is not just smelly, it can be dangerous, a health risk and een an explosive. If there is H2S in the water you will need to aerate the water to dissipate that gas before adding vinegar (or chlorine) to the water. - see CHLORINE SAFETY WARNING where we discuss both H2S and chlorine gas hazards.

The advice continues to explain that while some chlorine gas will form at pH 4.5 (you'll smell it), the addition of the chlorine raises the pH to a safe level - that is, the total quantity and duration of chlorine gas formation should be low. As you add chlorine the solution becomes alkaline.

Check the disinfectant solution pH again.

When ready for use, the disinfectant solution (water + chlorine) should have a pH between 6 and 7 to be most effective as a biocide.

Step by step well disinfection procedures using pH adjusted disinfectant solution are given in these two articles:

Chlorine & Well or Water Equipment Disinfection Solution pH Adjustment & Target References

  • Our REFERENCES for this article contain a complete list of citations; excerpts are shown just below
  • Ascenzi, Joseph M., ed. Handbook of disinfectants and antiseptics. CRC Press, 1995.
  • Bassett, D. C. J. "The effect of pH on the multiplication of a pseudomonad in chlorhexidine and cetrimide." Journal of clinical pathology 24, no. 8 (1971): 708.
  • Brodtmann Jr, Noel V., and Peter J. Russo. "The use of chloramine for reduction of trihalomethanes and disinfection of drinking water." Journal (American Water Works Association) (1979): 40-42.
  • Dailloux, M., C. Laurain, M. Weber, and P. H. Hartemann. "Water and nontuberculous mycobacteria." Water Research 33, no. 10 (1999): 2219-2228.
  • Fair, Gordon M., J. Carrell Morris, Shih Lu Chang, Ira Weil, and Robert P. Burden. "The behavior of chlorine as a water disinfectant." Journal (American Water Works Association) 40, no. 10 (1948): 1051-1061.
  • Hua, Guanghui, and David A. Reckhow. "Comparison of disinfection byproduct formation from chlorine and alternative disinfectants." Water Research 41, no. 8 (2007): 1667-1678.
  • Richardson, S. D., A. D. Thruston Jr, T. V. Caughran, P. H. Chen, T. W. Collette, K. M. Schenck, B. W. Lykins Jr, Ch Rav-Acha, and V. Glezer. "Identification of new drinking water disinfection by-products from ozone, chlorine dioxide, chloramine, and chlorine." In Environmental Challenges, pp. 95-102. Springer Netherlands, 2000.
  • Waltimo, T. M. T., D. Ørstavik, E. K. Siren, and M. P. P. Haapasalo. "In vitro susceptibility of Candida albicans to four disinfectants and their combinations." International Endodontic Journal 32, no. 6 (1999): 421-429.
  • Ward, N. ROBERT, R. L. Wolfe, and BETTY H. Olson. "Effect of pH, application technique, and chlorine-to-nitrogen ratio on disinfectant activity of inorganic chloramines with pure culture bacteria." Applied and environmental microbiology 48, no. 3 (1984): 508-514.
  • Wu, Wells W., Paul A. Chadik, William M. Davis, Joseph J. Delfino, and David H. Powell. "The effect of structural characteristics of humic substances on disinfection by-product formation in chlorination." In ACS SYMPOSIUM SERIES, vol. 761, pp. 109-121. Washington, DC; American Chemical Society; 1999, 2000.
  • Yu-sen, E. Lin, Radisav D. Vidic, Janet E. Stout, and L. Yu Victor. "Negative effect of high pH on biocidal efficacy of copper and silver ions in controlling Legionella pneumophila." Applied and environmental microbiology 68, no. 6 (2002): 2711-2715.


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