What are some of the best products to purify water for drinking when you have no power?

What works best for small amounts of water, that is easily portable?

What works best for large amounts of water purification, for every day use, over an extended period of time?

Keith

On all of my big hunting trips we have used the Steripen. He uses UV light to kill off all of the bacteria and germs. Great for smaller amounts of water. Normally just fill up a Nalgene bottle from my nearby creek and then use it. It doesn't work well in murky/cloudy water. So you would have to filter out or let the settlement settle to the bottom before using it in water like that.