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emergency water purification calculator - bleach

That's a cool little calculator and good info. I regularly calculate how many gallons of bleach per million gallons of water, but if I had to disinfect 10 gallons of water my calcs would be pretty inaccurate. I carry a chlorine test kit around, but only because I work in that industry and I'm a water geek. After the holidays I'll have to put the calculator to the test.
 
JCavSD, I'm assuming you're carrying the vial of paper strips that turn purple if there is chlorine in the water? The ones that darken if there is a higher ppm.

So what is the correct ppm for purified drinking water then? I have one of those kits and that might be handy to have to verify the water is properly sterilized.
 
For what we do the strips aren't accurate enough, so we normally use a digital meter. As a backup we have kits that use a reagent and a color wheel.

I did run some numbers today based on one gallon of household bleach for 3,800 gallons of water. This works out to be a dose of around 16 mg/L (aka parts per million). So, to give you an idea of what this means...Dose minus demand equals residual. Demand is the amount of chlorine it takes to kill all the bugs and end up with no chlorine residual left over. However, you always want to be left with a residual to prevent further contamination, so your dose must always be greater than your demand. In a potable water system a residual of around 2.0 mg/L is ideal (opinions vary). So, if your dose is 5.5 mg/L, and your demand is 3.5 mg/L your residual will be 2.0 mg/L. Clear as mud?

Basically a dose of 16 mg/L will probably be like taking a bazooka to a knife fight. However, without knowing the quality of the source water, it's probably better to be safe than sorry. For short term I wouldn't have a problem with it, but long term I'd be concerned about drinking any water dosed to this level without knowing the residual.

Overall a good site with good information. Two issues I do want to mentions... First, the article states that bleach purifies water, which is certainly does not (doesn't sterilize it either). Bleach is a disinfectant only. There are bugs, like crypto, that are resistant to chlorine. Bleach will not remove suspended or dissolved solids. Second, smelling bleach in water is not necessarily a good indicator of successful disinfection. Objectionable taste and odor (sometimes bleach-like, according to my nose) can also occur as chlorine is simply reacting with organic matter.

Told you I was a water geek. :)
 
Bleach (chlorine) smell in the water can also indicate the presence of high chloromines, the product of incomplete oxidation of organic compounds. You could have a high chlorine content (and smell), but still have a lot of untreated organic compounds in the water.

Crypto outbreaks have, in the past few years, been traced to several highly chlorinated residential swimming pools, so no, chlorine isn't an effective agent for killing crypto. It also doesn't remove heavy metals (arsenic, mercury, etc.)
 
Codger_64 said:
Crypto outbreaks have, in the past few years, been traced to several highly chlorinated residential swimming pools, so no, chlorine isn't an effective agent for killing crypto. It also doesn't remove heavy metals (arsenic, mercury, etc.)
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Exactly, and this is why I have issues with terms like purification and sterilization. It gives a false sense of security.

Actually the bleach smell in the presence of chloramines isn't typically cause by high concentrations, it's caused because the chlorine to ammonia ratio isn't idea...or improper breakpoint chlorination. If odor is present it usually indicates that not enough chlorine is being added.
 
but if I had to disinfect 10 gallons of water my calcs would be pretty inaccurate.
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I don't know what the difficulty is, standard treatment is 8 drops of bleach per gallon of water. Double this if water is highly suspect, there is obvious contamination, non-moving water, etc.

Chlorine will dissipate and leave the water OK to drink, just leave the cap off of your water container to allow this.
 
Drops per gallon will work fine for the short term. However, it's just a very loose and inaccurate methodology compared to what's used for disinfecting public drinking water. In a way your correct, chlorine will get used up over time (dissipate if you want), but with that so does the ability to disinfect. The idea is to not add so much chemical that it's unhealthy, but add enough to make the initial kill plus maintain a lasting residual. No residual = no disinfection = breeding ground for bacteria, viruses, and protozoa. This is the problem with bottled water. It's fine until you open the bottle, put your lips on it, and leave it in the car baking in the sun for a day. Whatever nasty lip junk you left on the bottle is now breeding like there's no tomorrow. Blah!
 
Jason, I plan on filtering my water first thru a .3 micron filter then bleaching. So the filter should catch the larger Protozoa.

Jason, I understood conceptionally what you're saying but can you break it down into really simplified terms for novice like myself...if I have a vial of those test strips that give a rough indication of the ppm could you tell me a safe range (low to high) what the ppm should be so I can match the purple colored paper to the color index. I realize it isn't going to be perfect but it will be a validation my drops per gallon mixture is close.
 
Quirt said:
Jason, I plan on filtering my water first thru a .3 micron filter then bleaching. So the filter should catch the larger Protozoa.

Jason, I understood conceptionally what you're saying but can you break it down into really simplified terms for novice like myself...if I have a vial of those test strips that give a rough indication of the ppm could you tell me a safe range (low to high) what the ppm should be so I can match the purple colored paper to the color index. I realize it isn't going to be perfect but it will be a validation my drops per gallon mixture is close.
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Well, chlorine won't kill everything, but filtering and chlorinating is about as good as you're going to get outside of boiling then adding a little chlorine. I think the website recommended thorough mixing and something like 30 minutes of contact time, which is a great idea. If, after that 30 minutes you have a residual of around 1 or 2 mg/L (ppm) it's probably going to be as good as it gets. As a general rule I think anything under 0.5 mg/L isn't enough...although from a regulatory standpoint 0.2 is acceptable. The maximum residual we're allowed to have in public drinking water is 4 mg/L, but for short term, considering that the dosing method isn't exact, I probably wouldn't have an issue with twice that residual. I've honestly never sampled anything over 3.7 mg/L so have no idea what it would taste like. So, from a regulatory compliance standpoint, 0.2 to 4.0 mg/L is what you want. From my standpoint (for what that's worth) it's far better to add more than not enough as long as you're dealing with short term exposure.
 
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Jason, I don' t want to hi-jack this thread, but I have a question for you since you sound like you know a thing or two about water. :)

I don't know anything about water purifiers that are on the market, but I need something to carry with me when I motorcycle camp. I got caught last summer in Canada without a good water source and nothing to purify it with. So I boiled everything that I used.

What types or kinds of purifiers do you consider necessary for treating unknown water sources?
 
DiverDn said:
What types or kinds of purifiers do you consider necessary for treating unknown water sources?
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Wish I had a good answer for you based on personal experience, but I don't. I motorcycle camp on a street bike, so usually have a potable source nearby. I tend to carry quite a but of water with me just in case. The few times I've been caught without I've boiled water for immediate use.

I can say that filtration alone may not do the trick, and chemical treatment alone may not do the trick, but used together they make a pretty potent combination. It's called a multiple barrier approach which is very common...almost the rule...for treating most public drinking water. The pore size of the filter does play a key role. Not at work today, so don't have reference material on-hand, but here's a link to the CDC website that addresses filtration. I'm assuming that the info is valid.

http://www.cdc.gov/crypto/factsheets/filters.html
 
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