# how many drops of bleach **URL:** \ **Category:** Factual Questions\ **Created:** [December 21, 2007, 12:15am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772 "2007-12-21T00:15:20Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![NadaHappyCamper](https://avatars.discourse-cdn.com/v4/letter/n/278dde/32.png) [@NadaHappyCamper](https://boards.straightdope.com/u/NadaHappyCamper)\ **Post date:** [December 21, 2007, 12:15am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/1 "2007-12-21T00:15:20Z")
how many drops per gallon of bleach do i use to make water safe to drink? ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [December 21, 2007, 12:26am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/2 "2007-12-21T00:26:06Z")
> [@](#): > > Bleach will kill some, but not all, types of disease-causing organisms that may be in the water. If the water is cloudy, filter it through clean cloths or allow it to settle, and draw off the clear water for disinfection. Add 1/8 teaspoon (or 8 drops) of regular, unscented, liquid household bleach for each gallon of water, stir it well and let it stand for 30 minutes before you use it. Store disinfected water in clean containers with covers. From [the EPA](http://www.epa.gov/safewater/faq/emerg.html). ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [December 21, 2007, 1:11am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/3 "2007-12-21T01:11:00Z")
In 1994 I was discussing this subject with somebody who worked for the National Park Service at Zion NP’s water treatment facility. When I opined that 50 – 100 ppm might be a suitable chlorination range for drinking water, he said that would probably not cut the mustard anymore and suggested a level of at least 200 ppm to kill hard-shelled microorganisms such as Cryptosporidium. I don’t remember what this translates to in terms of drops of bleach/gallon. More importantly, does anybody know the equation for how much hydrogen peroxide to add to _dechlorinate_ the water? I used to know it, but now I can’t remember. ---
**Author:** ![Bag\_of\_Mostly\_Water](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bag_of_mostly_water/32/1029_2.png) [@Bag\_of\_Mostly\_Water](https://boards.straightdope.com/u/Bag_of_Mostly_Water)\ **Post date:** [December 21, 2007, 2:55am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/4 "2007-12-21T02:55:36Z")
According to my calculation (and remember, I’m an ex-chemist), 8 drops per gallon works out to just under 10 ppm sodium hypochlorite (9.8 ppm, assuming “regular, unscented, liquid household bleach” is 6% sodium hypochlorite). By way of comparison, swimming pools are required to maintain between 2 and 4 ppm chlorine (sodium hypochlorite) for proper sanitation. This can be pushed up to 20 or 30 ppm under certain conditions (shocking when the high cyanuric acid level is high). 50 to 200 ppm for drinking water seems very high to me. ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [December 21, 2007, 3:41am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/5 "2007-12-21T03:41:56Z")
That sodium hypochlorite will happily react with whatever it can get to, producing oxygen and sodium chloride (plus oxides of whatever was available). That’s why the EPA recommendation is to let the water sit for a while before drinking. ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [December 21, 2007, 4:06am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/6 "2007-12-21T04:06:14Z")
[QUOTE=Ex\_Chemist] 50 to 200 ppm for drinking water seems very high to me. [/QUOTE] It’s very high—extremely high. It would burn your throat if you drank it—I speak from experience. That’s why I specifically mentioned dechlorinating the water with hydrogen peroxide to make it potable. Swimming pool levels of chlorination will make water just dandy to swim in, but it’s not going to kill Cryptosporidium or Giardia lamblia. So I reiterate: does anybody know how much hydrogen peroxide to add to chlorinated water to dechlorinate it? ---
**Author:** ![Szlater](https://avatars.discourse-cdn.com/v4/letter/s/90ced4/32.png) [@Szlater](https://boards.straightdope.com/u/Szlater)\ **Post date:** [December 21, 2007, 10:52am UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/7 "2007-12-21T10:52:39Z")
[QUOTE=Washoe] So I reiterate: does anybody know how much hydrogen peroxide to add to chlorinated water to dechlorinate it? [/QUOTE] NaOCl + H[sub]2[/sub]O[sub]2[/sub] → O[sub]2[/sub] + NaCl + H[sub]2[/sub]O So, I would guess that you should use equal amounts of bleach (NaOCl) and peroxide (H[sub]2[/sub]O[sub]2[/sub]). ---
**Author:** ![asterion](https://avatars.discourse-cdn.com/v4/letter/a/4da419/32.png) [@asterion](https://boards.straightdope.com/u/asterion)\ **Post date:** [December 21, 2007, 1:41pm UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/8 "2007-12-21T13:41:34Z")
[QUOTE=Szlater] NaOCl + H[sub]2[/sub]O[sub]2[/sub] → O[sub]2[/sub] + NaCl + H[sub]2[/sub]O So, I would guess that you should use equal amounts of bleach (NaOCl) and peroxide (H[sub]2[/sub]O[sub]2[/sub]). [/QUOTE] Taking into account that drugstore hydrogen peroxide is a 3% solution, of course. So adjust your amounts accordingly to get the same amount of moles added. ---
**Author:** ![Cowgirl\_Jules](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@Cowgirl\_Jules](https://boards.straightdope.com/u/Cowgirl_Jules)\ **Post date:** [December 21, 2007, 4:38pm UTC](https://boards.straightdope.com/t/how-many-drops-of-bleach/430772/9 "2007-12-21T16:38:34Z")
[QUOTE=Washoe] In 1994 I was discussing this subject with somebody who worked for the National Park Service at Zion NP’s water treatment facility. When I opined that 50 – 100 ppm might be a suitable chlorination range for drinking water, he said that would probably not cut the mustard anymore and suggested a level of at least 200 ppm to kill hard-shelled microorganisms such as Cryptosporidium. I don’t remember what this translates to in terms of drops of bleach/gallon. [/QUOTE] That’s really high. I run a small water system, and anything over 4 ppm of chlorine residual in the system is legally reportable as over the maximum contaminant level for California. You can definitely taste 2 ppm. When we install or repair mains, we disinfect to either 25 ppm or 100 ppm for a specified contact time, but we flush the line to get that out before it’s put back into the system. You don’t drink that level, and in fact, agencies are supposed to dechlorinate that flushing water to reduce the chlorine levels to where the sewer system or storm drain network can handle it. I chlorinate with gaseous chlorine, not hypochlorite, so I don’t know the dosage rates for that off the top of my head. My books are all more on the scale of 100,000 gallons of water, not one, so they won’t be too helpful to you. I’d go with the EPA’s cite.