Rain Water
https://grandpappy.org/hwater.htm
For the average person, the best source of replacement drinking water will probably be rain water. Although this is an excellent source of safe drinking water, it is unpredictable in regards to timing and quantity. However, for most people, this is probably the cleanest source of replenishment drinking water they will have access to on a regular but intermittent basis.
Regardless of where you live in the world, if you can catch the rain water BEFORE it comes in contact with anything, then it is safe to drink without any special treatments. Even when you take acid rain into consideration, this is still a true statement. However, if there is a nuclear, chemical, or biological war at some point in the future, then rain water may not be safe to drink for some period of time. You will have to use your own judgment in that situation. One of the portable commercial water filters described below would be appropriate in those types of unusual and hazardous situations.
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