Brian:

I cannot say for sure why exactly the Puritabs product was banned in the US, but I understand it may be due to the tablets effervescent action, which may produce chlorine gas! You can find some information about Puritabs at this link I have read where there is a controversy about Puritabs killing cysts and therefore it is recommended to use a carbon-based filter.

If you had the time and resources to do so, I noticed the enclosed link above mentions boiling the water as one of the best methods of water treatment. I have heard if you are camping and (in a non-urgent survival situation) wish to have the water for later then try this method.

For each Gallon of Water:

1. Boil the water for 5 minutes. Boiling this long does compensate for higher altitudes.
2. Let stand for 2 hours minimum up to 8 hours in direct sunlight. Use a glass container for this.
3. If water is really cloudy sift through a cheesecloth or similar material before boiling.
4. You can also add 4 drops per liter of sodium hypochlorite (e.g. Clorox) or a total of 16 drops minimum. Add the drops after removing the water from the heat source. Letting the water stand in the sun helps remove the "chlorine" taste.

There is another alternative product called Chlor-Floc and is marketed under the name of Watermaker. This is the current US Army issue water treatment system. Again, the army recommends using a filter. I hope this helps.

Take care,

Stargazer
"If we believe in absurdities, we shall commit atrocities - Voltaire"