This drinking water disinfection article gives the details of the amount of different types of disinfectant needed to treat drinking water - the disinfectant concentration needed to make water safe to drink.

We explain the increased treatment time or contact time needed depending on the actual chlorine concentration in different bleach products, the actual water temperature and depending on whether or not the treated water is cloudy.

This article series outlines methods to purify or sanitize drinking water in an emergency following a disaster such as an earthquake, flood, or hurricane.

How Much Disinfectant to Use in Drinking Water?

Article Contents:

• WATER DISINFECTANT CONCENTRATION - how much disinfectant to use
• WATER DISINFECTANT CONTACT TIME - how long to wait before drinking the disinfected water

What's the Concentration of Disinfectant Needed to Make Safe Drinking Water?

The amount of disinfectant needed to purify water depends on how contaminated the water is to begin with. If you are using liquid iodine and have no better authoritative information, try a teaspoon of iodine per gallon of water. Other experts recommend:

• Iodine in clear water:
  
  5 drops of 2% tincture of iodine per quart of clear water
• Iodine in cloudy water:
  
  10 drops of 2% tincture of iodine per quart of cloudy water
• Other water disinfectant products
  
   based on iodine: the label will indicate the number of capfuls of disinfectant to use per quart of water
• Iodine tablets,
  
  such as PotableAqua™ - (50 tablets per bottle) two tablets treats a quart of water and are effective against Giardia lambia.
  
  Also see the U.S. Army field manual FM 21-10 Chapter 2: Individual Preventive Medicine Procedures where preferred and alternative methods of emergency drinking water purification using iodine are discussed:
• Bleach for sterilizing drinking water:
  
  the number of drops of bleach to add per gallon of water depend on the percent concentration of the bleach product you are using. Let your bleached water stand for 30 minutes before using it.
  
  If the water does not have a slight "bleach" smell, repeat the dose and let the water stand for an additional 15 minutes. If you let the water stand longer the unpleasant bleach odor will dissipate completely.
  
  Definition of the EPA-recommended Superchlorination procedure for drinking water:
  
   the U.S. EPA recommends adding one teaspoon of chlorine bleach per ten gallons of drinking water in order to reach a chlorine concentration of 3.0 ppm in the drinking water. Use three teaspoons, or one tablespoon of chlorine bleach per 30 gallons of water to be treated.
  
  Watch out: not all bleach solutions provide the same concentration of chlorine, so just using one teaspoon of chlorine bleach per ten gallons may be unreliable. Use a chlorine test kit or swimming pool test kit
  
  to confirm that your superchlorinated drinking water has reached 3.0 ppm.
  
  See CHLORINE in WATER, HOW TO TEST FOR
  
  Watch out: the concentration of chlorine in drinking water after bleach has been added will not remain constant.
  
  The concentration is highest immediately after the chlorine-based bleach has been added to the water. When treating a quantity of drinking water (such as in an RV holding tank) or other container,
  
  see WAIT TIME & WATER TEMPERSTURE (just below in this article) or else wait six hours before testing to determine if the chlorine concentration is at 3.0 ppm.
  
  That wait time also gives more contact time to permit the disinfectant action of the bleach to destroy the organisms that are its target.
  
  
  • 1% bleach: use 40 drops of bleach per gallon of drinking water
  • 2% to 6% bleach solution: use 8 drops of bleach per gallon of water
  • 7% to 10% bleach solution: use 4 drops of bleach per gallon of water
  • Unknown bleach concentration (presuming this is store-bought laundry bleach): use 10 drops of bleach per gallon of water.
  • WELL DISINFECTANT pH ADJUSTMENT may also be necessary for effective water disinfection.

The table below is derived from U.S. Army field manual FM 21-10 Chapter 2: Individual Preventive Medicine Procedures

Wait Time & Water Temperature when adding a disinfectant, before drinking water

• Typical wait time before drinking treated water is at least 30 minutes
  
  from the time that the treatment tablet has become fully dissolved in the water. The necessary time could be longer.
• Water temperature should be 65 degF 
  
  or higher before treatment with bleach for best results. You may be able to warm your water by placing it in the sun. If the water is below 40 deg.F. you should double the wait time before consuming it.
• Water temperature should be 68 degF 
  
  or higher before treating it with iodine. Iodine is more effective than bleach in killing off Giardia contamination in water.
• Be sure to read the instructions.
  
  Iodine, bleach (sodium hypochlorite), or other water disinfectants will require some wait time to permit the chemical to act on water bacteria before the water can be consumed.
• Water Disinfectant Contact time:
  
  Using any chemical to sterilize water will require sufficient contact time between the chemical and the water before the water can be consumed. The chemical, bleach, or iodine, needs time to kill the microorganisms in the water.
• If you have iodine tablets
  
   intended for purifying water, the tablet bottle label should indicate the number of tablets to use per gallon of water and also the length of time that you must let the water sit before drinking it.
• If using liquid iodine to purify water,
  
  let the treated water sit for a day before using it to drink.
• If your water supply is very cold 
  
  you will need to increase the wait time for the chemical disinfectant to act before the water can be consumed.
• If your water supply is cloudy 
  
  you will need to increase the wait time for the chemical disinfectant to act before the water can be consumed. That's why experts recommend filtering the water with a clean cloth first if you can. In an emergency you might also be able to use clean coffee filters or even plain white paper towels.

Water Disinfection Does Not Remove All Contaminants

Municipal water supplies are generally safe as their water treatment efficacy is monitored regularly as required by federal regulations. But private water supplies may be unsafe and are almost certainly unsafe after disasters such as flooding.

Watch out: as we report throughout this article series, different disinfection methods vary in their effectiveness in combating different types of water contaminants. If you rely on a single disinfection method, for example chlorine disinfection, your water supply could still be contaminated by cryptosporidium, or if chemical contaminants are present, those, too, might remain.

Details are at WATER DISINFECTION LIMITATIONS.

Research on Drinking Water Disinfectant Quantity

• Arnold, Benjamin F., and John M. Colford Jr. "Treating water with chlorine at point-of-use to improve water quality and reduce child diarrhea in developing countries: a systematic review and meta-analysis." American journal of tropical medicine and hygiene 76, no. 2 (2007): 354-364.
• Aquamira™ chlorine dioxide water purification kits - see www.aquamira.com/
  
  Excerpt: Whether you are camping, traveling in a foreign country or faced with a disaster, our goal is to provide you with safe, pure and good tasting drinking water. Our complete line of water treatment products include leading edge purification and filtration technologies developed and tested in the lab and proven in the field. We offer systems and products that will provide water for a single individual or a village and almost anything in between.
• Ascenzi, Joseph M. (Editor), Handbook of Disinfectants and Antiseptics, CRC, 1995, ISBN-10: 0824795245 ISBN-13: 978-0824795245
  
  "The evaluation of chemical germicides predates the golden age of microbiology..." -
  This well-focused, up-to-date reference details the current medical uses of antiseptics and disinfectants -- particularly in the control of hospital-acquired infections -- presenting methods for evaluating products to obtain regulatory approval and examining chemical, physical, and microbiological properties as well as the toxicology of the most widely used commercial chemicals.
• Manci, Karen, "Bacteria in Drinking Water" - "Chlorine," Karen Mancl, water quality specialist, Agricultural Engineering, Ohio State University Extension. Mancl explains factors affecting the effectiveness of chlorine in water as a means to destroy bacteria and other microorganisms. OSU reports as follows:

  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. -- http://ohioline.osu.edu/b795/index.html is the front page of this bulletin.

• New England Journal of Medicine: City Hospital, Birmingham, UK. Covers the many methods of the elimination or prevention of microbial growth. Provides an historical overview, descriptions of the types of antimicrobial agents, factors affecting efficacy, evaluation methods, and types of resistance. Features sterilization methods, and more. Previous edition: c1999. DNLM: Sterilization--methods.
• Nieuwenhuijsen, Mark J., Mireille B. Toledano, Naomi E. Eaton, John Fawell, and Paul Elliott. "Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review." Occupational and environmental medicine 57, no. 2 (2000): 73-85.
• Peter Andrey Smith, "A Quest for Even Safer Drinking Water", The New York Times, 27 August 2013, p. D3
• Potable Aqua® emergency drinking water germicidal tablets are produced by the Wisconsin Pharmacal Co., Jackson WI 53037. 800-558-6614 pharmacalway.com
• Giardia exposure limits for drinking water: see www.mass.gov/dep/water/drinking/standards/giardia.htm is the current regulatory exposure limit (your minimum target for sterilization)
• Russell, A.D., (Ed.), W. B. Hugo (Editor), G. A. J. Ayliffe (Editor), Blackwell Science, Principles and Practice of Disinfection, Preservation and Sterilization (Hardcover)
  2004. ISBN-10: 1405101997, ISBN-13: 978-1405101998.
  
  The Pharmaceutical Journal: "This is an excellent book. It deals comprehensively and authoritatively with its subject with contributions from 31 distinguished specialists. There is a great deal to interest all those involved in hospital infection ... This book is exceptionally well laid out. There are well chosen references for each chapter and an excellent index. It is highly recommended."
• Starke, Jeffrey A., Dwight D. Bowman, Michael Labare, Elizabeth A. Fogarty, Araceli Lucio-Forster, Joseph Barbi, Michael B. Jenkins, Mary Pavlo, and Michael A. Butkus. DO IODINE WATER PURIFICATION TABLETS PROVIDE AN EFFECTIVE BARRIER AGAINST CRYPTOSPORIDIUM PARVUM? [PDF] Military medicine 170, no. 1 (2005): 83-86.
  Abstract:
  U.S. Army Iodine Water Purification Tablets were tested to determine their efficacy against Cryptosporidium parvum, a protozoan resistant to chemical disinfection.
  
  Purified oocysts in phosphate-buffered water were treated with varying concentrations of iodine or with iodine tablets as per U.S. Army protocol. Neonatal mouse pups were then each inoculated with 10,000 treated oocysts, and 1 week later scored as infected or uninfected.
  
  Watch out: Using this methodology, iodine tablets were found to be inadequate against C. parvum because the Army doctrinal dose of 560 mg min/L, calculated as 16 mg of I2/L and 35 minutes of contact time, showed less than 1 log inactivation. A dose of 29 mg of I2/L at the same contact time was required to achieve a 2 log inactivation.
  
  Excerpts from Discussion:
  These studies have shown that the current Army guidelines for use of the globaline tablets for the treatment of drinking water will not inactivate the majority of oocysts that might be present within contaminated water. Thus, the existing Army recommendations for water treatment may not be adequate to protect soldiers operating in an austere environment from developing infections from Cryptosporidium species.
  
  There was no effect observed on reducing infectivity using the tablets as prescribed by the manufacturer and the Army.
  
  This finding suggests that iodine tablets might be less effective in natural waters. An increase in iodine dose to at least 29 ppm (or 1,015 mg min/L) is required to achieve 2 log (99%) inactivation with iodine.
  
  Gerba et al.3 reported that increased contact times do not significantly increase the inactivation of the oocysts from 10% inactivation with a 20-minute contact time to 66 to 81% inactivation at a 240-minute contact time.
  
  Simply increasing the contact time for the iodine to inactivate oocysts does not seem to be a feasible solution to provide adequate protection.
  
• U.S. ARMY FIELD MANUAL 21-10, FIELD HYGIENE AND SANITATION [PDF] 1988, web search 07/02/2010, original source: http://www.enlisted.info/field-manuals/fm-21-10-field-hygiene-and-sanitation.shtml
  
  The purpose of this manual is to assist individual soldiers, unit commanders, leaders and field sanitation teams in preventing disease and environmental injuries. The manual provides information on preventive medicine measures (PMM) to the individual soldier as well as essential information for the unit commander, unit leaders, and the unit field sanitation team on applying unit level PMM.
  • FM 21-10 CHAPTER 1: INTRODUCTION TO THE MEDICAL THREAT [PDF]
  • FM 21-10 CHAPTER 2: INDIVIDUAL PREVENTIVE MEDICINE PROCEDURE [PDF]
  • FM 21-10 CHAPTER 3: LEADERS PREVENTIVE MEDICINE PROCEDURES [PDF]
  • FM 21-10 CHAPTER 4: UNIT FIELD SANITATION TEAM [PDF]
  • FM 21-10 APPENDIX A [PDF]
  • FM 21-10 REFERENCES [PDF]
  • FM 21-10 INDEX [PDF]
• Also see TECHNICAL REVIEWERS & REFERENCES at the end of this page

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

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• WELL DISINFECTANT pH ADJUSTMENT - needed for effective chlorination in wells
• WATER DISINFECTION LIMITATIONS

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