Cya in drinking water...

[Sunnydaze]

I'm sure this has been discussed before but i couldn't find an answer via forum search. The epa approved the use of dichlor and trichlor for disinfecting drinking water in 2001. Wouldn't cities which use dichlor or trichlor have some cya in their drinking water? I can't find maximum allowable amounts but it seems it's possible there could be cya in tap water, right?

A Drinking Water Relevant Water Chemistry Model for the Free Chlorine and Cyanuric Acid System from 5°C to 35°C | Science Inventory | US EPA

cfpub.epa.gov

"In July 2001, dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) and trichlor (trichloroisocyanuric acid) use for the routine treatment of drinking water in the United States (US) was first approved. Their use is equivalent to adding free chlorine (hypochlorous acid plus hypochlorite ion) and cyanuric acid in a fixed proportion. "

 

[Donldson]

I doubt many cities are using it, but since even if dichlor were used to bring the FC to 3 ppm then it would add 2.7 ppm CYA. So you'd need to have your pool evaporate about 5x over to get a measurable amount of CYA added to the water from it. CYA also naturally breaks down at a couple of ppm a month, that would probably be faster than it could be added from tap water that was sanitized with dichlor.

 

[JoyfulNoise]

Agreed. If you look at the specifics of the rulings, what is approved is the use of dichlor or trichlor as a disinfecting agent but most likely in the context of point-of-use systems, eg, disinfecting tablets for emergency water use. Municipal water suppliers will be unlikely to use either dichlor or trichlor as their control and dosing systems would be far more complicated to implement and very expensive.

As for toxicity, table salt is more toxic than cyanuric acid ...

 

[Griswald]

I see this all the time...people say that they are storing drinking water long-term and use a teaspoon of "pool shock" per gallon to get chlorine in it. I know CYA breaks down over time, but what does it leave behind that someone might drink?

 

[Sunnydaze]

I doubt many cities are using it, but since even if dichlor were used to bring the FC to 3 ppm then it would add 2.7 ppm CYA. So you'd need to have your pool evaporate about 5x over to get a measurable amount of CYA added to the water from it. CYA also naturally breaks down at a couple of ppm a month, that would probably be faster than it could be added from tap water that was sanitized with dichlor.

Agreed. If you look at the specifics of the rulings, what is approved is the use of dichlor or trichlor as a disinfecting agent but most likely in the context of point-of-use systems, eg, disinfecting tablets for emergency water use. Municipal water suppliers will be unlikely to use either dichlor or trichlor as their control and dosing systems would be far more complicated to implement and very expensive.

As for toxicity, table salt is more toxic than cyanuric acid ...

Makes perfect sense. Thanks!

 

[JoyfulNoise]

I see this all the time...people say that they are storing drinking water long-term and use a teaspoon of "pool shock" per gallon to get chlorine in it. I know CYA breaks down over time, but what does it leave behind that someone might drink?

If you follow drinking water standards and only add enough dichlor to achieve 1 to 1.5 ppm FC, then the amount of cyanuric acid added to the water is minuscule (less than 1ppm). It will have no physiological effect and since it’s not really absorbed well in the gut, you will pass most of it.

The problem is adding any kind of chlorine (liquid or solid) to untreated water (river water or unfiltered shallow well water). There is so much natural organic matter (NOM) in those kinds of water that chlorine from any source will form all sorts of nasty trihalomethane compounds that are NOT good for your health. Even sediments will quickly use up the chlorine and disinfection will be minimal. This is why many emergency kits use iodine as a disinfection agent - it can kill pathogens and it doesn’t generate some of the nasty disinfection by-products. Your body can also utilize iodine.

So it really depends on the details. If you store a couple of gallons of filtered water and add a few granules of dichlor to it, no big deal. If you scoop up green fetid water out of a pond and expect to make drinkable with a dash of pool shock, you’re in for a nasty surprise.

 

[Griswald]

If you follow drinking water standards and only add enough dichlor to achieve 1 to 1.5 ppm FC, then the amount of cyanuric acid added to the water is minuscule (less than 1ppm). It will have no physiological effect and since it’s not really absorbed well in the gut, you will pass most of it.

The problem is adding any kind of chlorine (liquid or solid) to untreated water (river water or unfiltered shallow well water). There is so much natural organic matter (NOM) in those kinds of water that chlorine from any source will form all sorts of nasty trihalomethane compounds that are NOT good for your health. Even sediments will quickly use up the chlorine and disinfection will be minimal. This is why many emergency kits use iodine as a disinfection agent - it can kill pathogens and it doesn’t generate some of the nasty disinfection by-products. Your body can also utilize iodine.

So it really depends on the details. If you store a couple of gallons of filtered water and add a few granules of dichlor to it, no big deal. If you scoop up green fetid water out of a pond and expect to make drinkable with a dash of pool shock, you’re in for a nasty surprise.

I believe most are referring to storage of potable water. I have a small "off grid" cabin on some land with no source of fresh water, so I've done lots of research on how to keep water there. Lots of "prepper" type web sites out there. Currently, I have a case of bottled water but nothing else.