the reason you boil water longer is to allow for impurites to settle out of the water sure the water may be safe from any parasites but there are impurities in water that may make you sick

I seriously question the validity of that statement. Please provide a reference that corroborates your claim. In my experience, raising the temperature of water tends to allow more impurities to go into solution, which would preclude separation by settling. I know of very few substances that precipitate out of solution as the temperature increases, unless you are referring to evaporation, in which case you would be losing clean water to the atmosphere, and concentrating the solution to the point that it exceeds the saturation point.

I don't think crypto spores can reliably be destroyed just by bringing the water to a boil. It takes some time at high heat to break down the spore compared to just trying to denature some "naked" protein. I think crypto is the primary reason for maintaining the boil for some time.

Keep in mind that the size of the container, the amount of water in the container and the surface area (or better yet the amount of contact area the bottom of the container has with the heat source) will determine when the water is adequately “mixed” to reach killing temperatures for pathogenic organisms and parasites. That is why many references say a “rolling boil”/large bubbles, indicating there is sufficient mixing of the water to reach killing temperatures in all parts of the container. A very deep pot/cup with only small bubbles may have water at the surface, which has not reached high enough temperatures to kill certain organisms.

Recognizing that most pathogenic bacteria are likely killed when the water reaches a rolling boil, most steam autoclaves (steam under pressure is far more efficient at killing, then boiling) operate at 250 F (well above 212F) under 15psi and the minimum autoclaving time is 15 minutes (although this is in part to allow steam to access all parts of the chamber).

I can tell you from personal experience, we use chemical (and biological indicators) integrator strips, which start to measure a given/standard heat (250F) over time. The use of chemical change tape (you may see these on surgical supply packs or other medical devices and supplies), which changes as soon as the given/standard temperature (250F) is not a valid indicator of sterilization. I have run studies in which autoclaving (at 250F under 15psi) for up to 10 minutes was insufficient to kill indicator bacteria (spore forming rods – a heat resistant Bacillus species), despite the change of the indicator tape.

Also keep in mind there is both heat labile (easily destroyed by heat) and heat stabile (resistant to heat inactivation or denaturing) bacterial/fungal toxins (proteins). When one is heating food/water, one is not only attempting to kill the living organisms, but also the toxins (both exo and endo) produced by the bacteria, both living and dead). It is possible the references to boiling water longer then either a rolling boil or for 1 minute are taking the presence and heat resistance of any bacterial toxins that might be present. While I have never heard of bacterial toxin poising from water (food – definitely yes), I guess it could be possible if there were a lot of organic material supporting bacterial growth.

Although, it is interesting that UV water purification devices such as the Steri-pen do not address or take into account any residual bacterial toxins. The MIOX solution might have some inactivation effect on toxins (I really do not know), but certainly filters with charcoal beds and boiling should be considered for water where the possibility of residual bacterial toxins could be present.


Pete

Also the turbulence from boiling will tend to keep things stirred up.

Strange that they don't even mention using chlorine when its the most readily available chemical treatment.

From the WI Dept. of Natural Resources (http://www.dnr.state.wi.us/org/water/dwg/Crypto.htm):
"Treating drinking water using normal doses of disinfectants such as chlorine does not kill Cryptosporidium oocysts. Researchers have found it takes 90 minutes to kill 90 percent of Cryptosporidium oocysts in a water sample treated with 80 milligrams of chlorine per liter of water. Normally, chlorine is applied at about one milligram per liter. Stronger disinfectants, such as ozone, do a better job of killing these protozoans in a shorter time."

From the Center for Disease Control (http://www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/factsht_cryptosporidiosis.htm):

"If you are unable to avoid using or drinking water that might be contaminated, then you can treat the water for Cryptosporidium by doing one of the following:
* Heat the water to a rolling boil for at least 1 minute. OR
* Use a filter that has an absolute pore size of 1 micron or smaller, or one that has been NSF rated for "cyst removal."

"Do not rely on chemicals to kill Cryptosporidium. Because it has a thick outer shell, this particular parasite is highly resistant to disinfectants such as chlorine and iodine."

p.s. The CDC says Giardia is also moderately chlorine-resistant but is killed or at least inactivated by boiling.

Sue

MIOX works well against crypto. that's why most municipal treatment plants use it instead of Chlorine now.

The 1 micron filter tip is an important one. Ever looked at filter specs? Very few of them meet the 1 micron recommendation.

Water temperature will not exceed it's boiling point unless under pressure; the boiling point drops as atmospheric pressure drops (e.g. when hiking/camping in high mountains).

I too have heard, "big bubbles, no troubles." The article at http://www.survivaltopics.com/survival/how-long-do-you-need-to-boil-water/ seems to bear this out.

In an urban survival situation, boiling is a dang good idea, although it won't remove chemical pollutants, heavy metals, etc.

In wilderness areas in North America, the water is generally safe to drink without treatment. The majority of girardia cases are generally caused by poor hygiene. Yes, this isn't what is generally accepted, but I've read the studies. However, having read the studies, I continue to treat my water. The cost of treatment is low, but the consequences of being wrong are high -- particularly in a survival situation. My point is this: hygiene, particularly hand washing, is as or more important as/than water treatment.

"...hygiene, particularly hand washing, is as or more important as/than water treatment."

That is probably true, but... what if you're washing your hands with (organically) contaminated water?

Sue