Making Water Potable with Bleach


Several years ago, there was an Expedition journal issue with the dilution for adding bleach to water to make it potable, but not so much bleach that it wasn’t.

My friend filled his 25 gal tank with questionable water and we want to make sure it’s drinkable.

If you look online, you mostly get bleach ratios for winterizing or sanitizing tanks. Anyone know the proper bleach to water ratio?

Roger M.

Technology has come a ways beyond adding regular laundry bleach to your drinking water. Dissolved chlorine is typically what your local water supply folks add to the drinking water for a city water system.
For travellers and overlanders, and using only salt, this small device generates that pure dissolved chlorine for making safe drinking water by stripping electrons from a brine mixture made with regular table salt and water ... and it does so for a purchase price of around a hundred bucks.
Although useable by itself, when used along with a decent filtration system, you can turn filthy pond water (or any water) into water that's as pure as that which you might find at your kitchen tap, or by purchasing water from a store.
Of course, being chlorinated, that water you've just made will now be safe for drinking for six months or more.
Generally speaking, this is a much better water purification solution than laundry bleach ... and it's only a hundred bucks to purchase, and uses a couple of pennies worth of salt per 20L of water purified.



There are several ways to make your water potable. Bleach is an option but not my first, second or third choice. Had a guy use scented bleach in a "Water Buffalo" (water trailer) and it was not drinkable.

However, according to "TB Med 577"

"d. Chlorine bleach. (1) In emergency situations, when calcium hypochlorite is not available for disinfection of bulk supplies, standard chlorine bleach (unscented sodium hypochlorite) can be used in its place. Bleach is normally a 5 percent or 50,000 mg/L chlorine solution. Add two drops of bleach per quart of water to be disinfected and let it stand for 30 min before drinking. If a dropper is not available, wet a cloth or stick with bleach and allow it to drip into the water. (2) For a 70-oz reservoir, use four drops from a standard 10-milliliter (mL) dropper or six drops for the 100-oz reservoir. Mix the added bleach in the reservoir water and let it stand 30 min before drinking it. (3) See appendix I for the amounts of bleach needed to disinfect larger volumes of water. Always allow at least 30 min for contact time."

Pacific Northwest yetti

Expedition Medic
CDC, and WHO also have posted ratios.




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We chlorinate all of our water, including washing water as that can be a source legionnaires disease which can be transmitted to the lungs during a shower.
Finding sodium hypochlorite (the active ingredient in household chlorine bleach) that is not contaminated with other "stuff" is sometimes difficult, so we often use liquid swimming pool chlorine which is typically 12% sodium hypochlorite compared with 5% in household bleach. The addition rate needs to be adjusted accordingly. We typically add 5-10ml per 100L, more for poor quality water.
Chlorine breaks down and disappears quite quickly in water (a matter of a few days), especially if the water is contaminated and especially in higher ambient temperatures, so re-dosing regularly is necessary.
Part of our treatment of potable water is a 0.5um carbon block 10" filter which will remove any residual chlorine (and other pathogens), at the tap, immediately before consumption.
OKA196 motorhome


Roger M.

If your chlorinated water is kept in a full, completely sealed, completely opaque container, it can last up to six months or longer.
Because Recreational Vehicles water tanks are vented, those tanks contain copious amounts of air, and therefore won't meet the "completely sealed" requirement, thus the chlorine will dissipate from the water at an accelerated pace.

Just an aside too, that laundry bleach is ineffective at killing Cryptosporidium, but the H2gO Global device I linked to above does kill Crypto. To clarify, the laundry bleach would eventually kill Crypto after multiple doses, but those multiple doses would render the taste unbearable.
The H2gO device also requires multiple dosing's, but because it imparts no perceptible "flavour" to the water, the water remains eminently drinkable.

Worth mentioning here too is that, although the Center for Disease Control does recommend laundry bleach as a method of purifying water in an emergency, the CDC recommends against it for general drinking water needs.
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