Friday, April 24, 2020

Purifying Water with Bleach, part 2

Not actually Erin.
& is used with permission.
Last month I was asked about how to purify stored water. This woman's concern was that the water was good enough coming out of the tap, but she was worried that long-term storage would result in bacterial growth which would render the water undrinkable.

Purification of water is something that we've covered extensively on this blog, and one of the earliest articles we made on that topic was Chaplain Tim's essay on using bleach to neutralize a toxin produced by an algal infestation of Toledo's water supply.

While filtration and boiling are still the best and easiest methods to purify water, sometimes they just won't work, as in the Toledo case. In that situation, the toxin was left behind by the algae as it died off, and even though filtration would remove the algae itself it would still leave the toxin behind. Worse, boiling the water would concentrate the toxin, actually making the problem worse!

I encourage you all to go read Tim's article, as it explains the chemistry behind why this works and how you should use it. Still, if you're like me and your eyes get a bit watery at all the math, I present to you this handy cheat sheet for storing and purifying water.

I don't recall where or when I found this image; all I know is that it was years ago during a web-wander. If you know where it's from, please let me know so I can give credit where due.

I added my own notes to this to enhance usability. We have teaspoons in my kitchen, but not 1/4 or 1/8 tsp and I don't trust my eyes to be able to accurately eyeball those amounts, so I used Tim's math from his post to convert their measurements into units I could use, which were drops.

Please note: This chart is for standard bleach, not concentrated bleach! Concentrated bleach is 8.25% NaClO (sometimes listed as Sodium hypochlorite) instead of the standard 5 to 6% solution, so you need to use less of it. According to his article, it's 4 drops of bleach to the gallon for clear water instead of the listed 8.

A few things I want to point out before I wrap this up:
  • Cloudy water is treated the same way as clear water because, as the text above indicates, you need to filter cloudy water before drinking it. 
  • If for whatever reason you can't filter it, I would treat it as surface water. 
  • Surface water gets special treatment because there's no telling what's in it. See this article for more explanation. 
  • Cold water needs more bleach because the cold inhibits chemical reaction. For a great example of this, do an experiment: take two mugs of water, one from the tap and one hot from the kettle or microwave, and stir in an equal amount of powdered coffee or cocoa. Watch how the hot water absorbs the powder easily, while the cold water causes the powder to clump. The same principle applies here. 
  • Allow at least 30 minutes for the bleach to do its job! If the water is cold, make that 60 minutes. 
  • The human nose can smell chlorine in water at a ratio of 3 parts per million. A ratio of chlorine to water which makes it safe to drink is 5 ppm. Therefore, if you can easily smell the chlorine without it being supter-strong, it's safe to drink. 
  • Chlorine loses its effectiveness years, becoming inert in 5 years. Powdered bleach lasts longer, although I don't know by how much. Here are directions on how to make your own bleach, although be advised that it will be more diluted than commercial versions. 

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