WM sells both Iodine and Halazone tablets. I remember Iodine tabs from the army... the bottle went in the little side pocket of the canteen/canteen cup cover. It had a waxlike something around the rim of the cap to keep moisture out.

I recall reading Ivan had a purifying tablet as well, smelled strongly of chlorine, and acted on precipitating impurities to the bottom of a container or hole. Probably chlorine dioxide or similar.

Katadyn is a big name in field water filtering. As much as they cost, small wonder.

As much as I like PMs, I have to say it... water is the REAL gold. Don't mess about on the cheap on purification methods if it is the stuff you'll be drinking.