Urgent: How much Bleach, or Iodine does it take to kill bacteria from lake water?

I used to do a bit of backpacking. I had 2 1-quart Nalgene (plastic) bottles. I put 2 or 3 drops of bleach in a quart of water. In a half hour it is drinkable as far as the little critters go. When 1 bottle is empty refill it, it should be ready by the time the other one is empty. If it was cloudy I would filter it through a bandanna over the mouth of the bottle. Never did get sick.

P.S. Please take a moment to award a "Best Answer" to one of those who answers your question. Not necessarily mine, but one of those who took their time to try to help.

To purify water for drinking purposes you can add 1/4 teaspoon of bleach per gallon of water.

This assumes you are using standard household bleach which is usually around 8.25% chlorine and that the water appears fairly clean to begin with. If the water is cloudy or muddy then you should filter it first.

Better option would be to boil it.

You best get professional help and look it up online. I'm sure there are professional products that don't involve bleach.