Two Letters Re: Seeking Advice on Swimming Pool Chlorine for Treating Drinking Water

Your advice is excellent; however, one of the best tools to have for checking [water] sanitation levels is a DPD [Diethyl-paraphenylene diamine reagent] test kit available from Taylor or Hach, to name a few.
I do not recommend OTO [orthotolidine reagent] kits as they are not as accurate as DPD. A 5mg/L initial shock should take care of most contaminants.
After you have treated any water with bleach, it should be tested for free chlorine residual after 30 minutes of contact time. Water with a free chlorine residual of 4 mg/L should not be ingested for long durations as it can cause mild digestive tract issues.
NOTE: The suggested residual is between 0.5 and 1.0 mg/L (parts per million or ppm). The EPA requires all discharge to have less than a 1.0mg/L free chlorine residual before
leaving the process flow.
The great thing about chlorine is that it will kill 95+% of all the biological contaminants; however, chlorine cannot kill giardia cysts as their outer covering is very difficult to break down. One other potential problem with the use of chlorine to treat surface water is the formation of bromide compounds which are cancerous; however, unless the precursors, carbon compounds, are present the formation rate is very low. If you are treating a contaminated well, the chance of bromide formation is even lower.
If you can pre-filter and add bleach to your water then allow the free chlorine level to drop to 0.5mg/L, placing the treated water in an opaque, sanitized vessel for long periods of time should be fairly safe as long as the initial feed stock was fairly free of organic matter to begin with. Thank you for all your hard work keeping us prepared for what ever may come. Sincerely, – Drew

Using calcium hypochlorite to disinfect water is a good idea. However, rather than trying to dump some amount of pool shock chlorine into a tank and hoping that it dissolves and mixes with the water, a better idea is to mix a slurry of it in a plastic bucket (it will corrode a metal one) and pour and mix the slurry.
Also, the halide (halogen, chlorine or iodine ions) need to be in contact with the water for some amount of time before they can kill all the bacteria – and that time is dependent on the temperature of the water. Colder water takes longer.
To test the degree of halogenation in water, I suggest that people get a pool water test kit and use it. They are very inexpensive, and easy to use: Simply get a (clean) bucket of water that’s been treated, and use the pool water test kit (for halogenation), ideal ‘pool water’ is about 2 parts per million (ppm) chlorine, drinking water should be between 2 and 5 ppm when treated – the chlorine will gas off over time, as long as the water isn’t likely to be re-contaminated (in an open top tank, for example) it doesn’t really need to be retreated. Dump the ‘test’ water out, [orthotolidine] OTO isn’t too good to drink.
The test kit will have directions but basically you put the test water into a clear chamber, add a reagent–usually orthotolidine (OTO)–to the chamber, and compare the color to the provided chart. If the water tests too low, add more slurry, if too high, next time don’t add so much. People will be able to figure out the approximate ‘right’ amount pretty quickly.
The military chlorination kits (for Lister bags and water buffalos) suggest as much as 10 ppm. This is to allow for high levels of organic material in the water (which adsorbs the chlorine, keeping it from disinfecting the water, and allowing the water to not be retreated too quickly); you probably recall drinking beverages so treated with as much fondness as I do. – Flighter [His article follows]

How to Disinfect Water, by Flighter

How to sterilize water? Simple: You don’t need to ‘sterilize’ water. Sterilization is the destruction of all microorganisms in, on and around an object. What is needed, is disinfection (killing of pathogenic (disease causing) organisms).
Disinfection can be done many ways, including filtration, heat, ozonation, and chemical disinfection.
Despite many stories to the contrary, simply boiling water will disinfect it. At any elevation you’re likely be at the boiling point of water is high enough to kill (or denature) anything in the water. You don’t need to boil it for any particular length of time, just get it boiling at a good rolling boil.
Filtration is a good method, you should use a filter that has an absolute rating of 0.2 micron diameter or less (0.1 micron). Personally, I use iodine crystals (Polar Pure first, then filter the water.
Chemical disinfection is the use of various chemicals (usually a halide like chlorine or iodine) in the water. It’s usually a quick, economical and effective method.
Here is a summary of water disinfection chemical usage based on the Wilderness Medical Society Practice Guidelines 2nd Edition, edited by William Forgey, MD (page 63):
For chemical disinfection, the key is the concentration of halogen, in parts per million (halogen to water):

Concentration of Halogen

Desired Concentration Contact time
@ 5oC / 41o F
Contact time
@ 15o C / 5o F
Contact time
@ 30o C / 86o F
2 ppm 240 minutes 180 minutes 60 minutes
4 ppm 180 minutes 60 minutes 45 minutes
8 ppm 60 minutes 30 minutes 15 minutes

How to get the desired concentration of halogens, for various products:

Iodine tablets, also known as: tetraglycine hydroperiodide; EDWGT (Emergency drinking water germicidal tablets); USGI water purification tablets; Potable Aqua (trade name); Globaline (trade name):
4 ppm – 1/2 tablet per liter of water 8 ppm – 1 tablet per liter of water.

NOTE: These tablets should be gunmetal gray in color when used – if rust colored, they are useless:
The free iodine has combined with atmospheric moisture. The bottles should be kept well sealed and replaced often. Checking the tablets in the bottle just exposes them to moisture in the air.For 2% iodine (tincture of Iodine) (gtts=drops)
4 ppm – 0.2 ml (5 gtts) 8 ppm – 0.4 ml (10 gtts)
NOTE: Tincture of Iodine should not be used as a wound treatment, so this is not a good option for a ‘dual use’ item.

10% povidone-iodine solution (Betadine)
NOTE: Solution only, not the “Scrub”variety – Since Scrub has soap in it
4 ppm – 0.35 ml (8 gtts) 8 ppm – 0.7ml (16 gtts)

Saturated (in water) Iodine crystals (Polar Pure ™)
4 ppm – 13 ml 8 ppm – 26 ml

Iodine crystals in alcohol
0.1 ml / 5 ppm 0.2 ml / 10 ppm

Halazone tablets (Monodichloroaminobenzoic acid)
4 ppm – 2 tabs 8 ppm – 4 tabs
NOTE: The old Vietnam era chlorine tabs are decades out of date. Chlorine tabs decay even more rapidly than iodine tabs. Not recommended.

Household bleach (Clorox™)
4 ppm – 0.1 ml (2 gtts) 8 ppm – 0.2 ml (4 gtts)
Note: Bleach offers a relatively economical method of treating large (gallons) of water at a time. 4 liters is approximately 1 gallon.
For very cold water contact time should be increased.

If drinking this water after disinfection, flavoring agents (drink mixes, etc) can be added: This must be done after the period allocated for disinfection ([otherwise] the disinfecting agent will bind to the organic material and not work).