It's not all or nothing sometimes

Mayberry and Hilljack both brought in cautionary tales concerning the use of bleach as a water purification scheme.  Sorry folks, but as chemistry is my professional metier, gotta set you straight on this one.

In a nutshell, the bleach loses around 20% of it's active ingredient (hypochlorite ions) every year.  If you leave it out in the noontime sun, you will accellerate this process, so don't leave it out in the sun.  

From the Chlorox company please read the following

When bleach and water are mixed together to create a cleaning or disinfecting solution, the solution is only good for 24 hours. The temperature of the water does not affect the cleaning or disinfecting abilities of the solution. After the 24 hours, the solution begins to lose needed disinfecting properties. Therefore, it is recommended that for disinfecting purposes, the solution is made fresh daily.

Our bottles do not have an expiration date, however, they do have a production date. Once you understand how to read the production date, you can decipher the shelf life of the bottle. Please look below for a chart explaining our production codes.

CODE	PLANT	YEAR	DATE
MD21002	MD2	1= 2001	002nd day of year
A90288	A9	0= 2000	288th day of year

We recommend storing our bleach at room temperatures. It can be stored for about 6 months at temperatures between 50 and 70 degrees Fahrenheit. After this time, bleach will be begin to degrade at a rate of 20% each year until totally degraded to salt and water. Storing at temperatures much higher than 70 degrees Fahrenheit could cause the bleach to lose its effectiveness and degrade more rapidly. However, if you require 6% sodium hypochlorite, you should change your supply every 3 months. 

Now, I cribbed the following from the chlorox site.  It is the classic use of chlorox to purify water:

In an emergency, think of this (one gallon of Regular Clorox Bleach) as 3,800 gallons of drinking water.

When the tap water stops flowing, Regular Clorox Bleach isn't just a laundry-aid, it's a lifesaver. Use it to purify water, and you'll have something to drink.

It's the same in any natural disaster. As the shock wears off and the days wear on, the biggest demand is for drinking water. Time after time, relief crews hand out free Clorox Bleach with simple instructions: use it to kill bacteria in your water and you'll have purified water to drink. Here's how: (Store these directions with your emergency bottle of Clorox Bleach.) 

First let water stand until particles settle. Pour the clear water into an uncontaminated container and add Regular Clorox Bleach per the chart.* Mix well. Wait 30 min. Water should have a slight bleach odor. If not, repeat dose.  Wait 15 min. Sniff again. Keep an eyedropper taped to your emergency bottle of Clorox Bleach, since purifying small amounts of water requires only a few drops. See chart* suggestions for storage bottle replacement.

Don't pour purified water into contaminated containers. To sanitize water jugs first, see instructions** at right.

Without water and electricity, even everyday tasks are tough. In lieu of steaming hot water, sanitize dishes with a little Clorox Bleach. Just follow the directions below to keep dishes clean.

Whether you use Clorox Bleach in an emergency or for everyday chores, it's always an environmentally sound choice. After its work is done, Clorox Bleach breaks down to little more than salt and water, which is good news anytime. 

*Ratio of Clorox Bleach to Water for Purification

2 drops of Regular Clorox Bleach per quart of water

8 drops of Regular Clorox Bleach per gallon of water

1/2 teaspoon Regular Clorox Bleach per five gallons of water

If water is cloudy, double the recommended dosages of Clorox Bleach.

(Only use Regular Clorox Bleach (not Fresh Scent or Lemon Fresh). To insure that Clorox Bleach is at its full strength, replace your storage bottle every three months.) 

**(Clorox Bleach Sanitizing Solution) 

Mix 1 tablespoon Regular Clorox Bleach with one gallon of water. Always wash and rinse items first, then let each item soak in Clorox Bleach Sanitizing Solution for 2 minutes. Drain and air dry.

So, folks are out there saying to themselves:  We can't use that, that stuff is crap, it goes bad after six months.  Wrong.

The truth of the matter is, you just need to have enough hypochlorite ions hanging about in you water to kill the nasty critters.  As the Clorox gets older, you just have to use a bit more.

So, in essence, after six months, the chlorox only has 90% of it's full-strength hypochlorite ions available to you.  

SO:

If the chlorox was made six months or less from the date you are using it, go ahead and use it as shown.  8 drops per gallon of water.

Now after six months, the stuff has between 80% and 90% of the hypochlorite remaining.  so I would say you have to guess on the conservative side and figure 80%.

so to treat a gallon of water, instead of 8 drops per gallon you will have to fudge a bit

8 drops divided by 0.8 = 10 drops of clorox

between 12 months and 18 months

8 drops divided by 0.7 = 12 drops of clorox

between 12 months and 18 months

8 drops divided by 0.6 = 14 drops of clorox

Now, some folks will worry that the Clorox will break down into something that will turn your children into mutant biker zombies (Remember, it is rap music that does that)....don't sweat it, it just breaks down into salt and water.

So, it appears to me that you just have to adjust the dose for older chlorox.  You don't toss it, that would be wasteful.  Just remember the kinetics of the stuff.  

And get a bunch of Britta filters to take care of the taste