Just registered here, and wanted to run a few ideas by people for survival-situation water purification. I've never seen these mentioned in survival guides, so I thought it'd be nice to get some feedback.

1. Quicklime: Quicklime has been around since paleolithic times. It is produced by "burning" limestone. The process takes a very hot fire (825C) -- you usually need a billows or other way to provide extra oxygen, but you don't need charcoal or coal. A primitive kiln (clay or mud bricks) helps, but isn't necessary if you have good airflow. The lime was usually cooked on a flat rock. The result is a caustic, hydrophilic powder that used to be used as a whitewash, in making cornmeal, and a few other things. Quicklime is interesting because it is a flocculant -- a chemical that encourages microscopic particles to coagulate and settle. It's not a very powerful flocculant, but it is used in some water treatment systems in various parts of the world; it not only helps settle bacteria, virii, and "gunk", but even heavy metals like arsenic, lead, etc. There are better natural flocculants (like alum, a major component of many of the latest water purification tablets (for example, PUR); also, iron chloride, iron sulfate, and a number of others), but they're rarer; limestone is all over the place and is easily recognisable.

2. pH adjustment: This, too, is used in some water treatment systems, but usually only on a small scale. Many disease-causing bacteria and virii are very pH-sensitive; exposure to particularly acidic or alkaline environments for lengths of time can kill them or otherwise render them inert. Quicklime is one way to significantly raise pH, but wood ashes can raise it and are much more readily available. I'm not sure of any convenient, safe ways to significantly lower pH unless you're in an area where there is abundant citrus. A downside to this concept is that you'll be drinking whatever you adjust the pH with. Ashes are mostly harmless, and you may be able to filter out much of the ash, but it still wouldn't be tasty.

3. Artificial artesian spring: I once read about this concept being used in rennaisance Italy. It would only be worthwhile if you were going to be in an area for a long time. The idea was that they dug a pit, lined it with material that was relatively water-impermiable, then filled it all up with clay, gravel, and sand except for a "well" in the center. Ideally, the well was lined with a relatively impermiable material as well They'd dump dirty water in the area around the well (which used to be the pit), which would filter through the clay and sand, straining out any contamination, and eventually seep into the base of the well. They could then gather the purified water from it. There might be situations where such a setup might have formed naturally (rock pit filled with dirt), wherein you'd only need to dig the well, although I'm not sure how one would identify such a situation effectively.

Thoughts? Ideas?