Thermal Death point: killing germs etc.

I thought I already posted this, But I don't see it? Oh well... Treating water with Chlorine doesn't kill all the bad stuff (e.g. Giardia or Cryptosporidium cysts), especially at cooler temps. Iodine kills only some of them. By definition A filter can not filter out viruses. So my question is: What temp will kill everything alive in the water. And, do I have do more than just bring it to a boil? What If I'm at 5000 feet where the boiling temp of water is 203F? Typically when cooking I use untreated water that I barely bring to a boil before dumping in dinner. I haven't ever been sick from it that I know of.

Morning, I can't remember the temp, but I have seen on one of the forums I belong to, that just bringing it to a boil, the critters are killed off by then, so even where the FS recommends boiling water for "x" minutes, it is over kill.

I've read that at altitude, where water boils at a lower temperature, you should boil for 5 minutes.

The rolling boil for 5 minute thing seems to be a belt-and-suspenders approach. The World Health Organization recommends bringing water to a boil as an indication that a high enough temp has been reached but all the bad bugs are dead after a few minutes at 160 deg F. Link
Not that's totally sterile at this point but anything that will make you sick is dead or deactivated. I figure by the time I see bubbles forming the water is safe.

My handy US Army Survival Handbook recommends 1 minute of boiling at sea level, adding 1 minute for each additional 300 meters of elevation, or just boiling for 10 minutes wherever you are in the world.

I've heard that water purification beyond filtering, using chemical tablets, or simply bringing water up to a boil then stopping, is usually overkill here in the states. The nasties that aren't killed by these methods are usually only present around third world countries. I don't know how true that is.

In the absence of a thermometer, a rolling boil is the only way to judge water temp accurately. That's the real reason for appealing to it.

Water boils at 212F at sea level and 203 at a mile. Water above 70C (158 F) will kill most water-bourne pathogens. However, it takes a few minutes, so taking the time to bring water to a boil and letting it cool to a drinkable temperature finishes the job. There are a few nasties that will survive such as botulism, but it is a problem only if you are canning something - not in your regular cooking.

I thought chlorine does kill the nasties. The temperature thing is simply a time factor - the cooler the temperature the longer you have to wait.

Boiling for 10 minutes does not make sense to me unless you want to cook the nasties for supper. The water does not get any hotter after boiling starts. A rolling boil should indicate that all water is of the same temperature. When you dump crabs in a pot they are dead quite quickly. Are viruses and bacteria different?

The problem is at altitude water boils BEFORE 212degrees, hence the longer recommended boiling time.

AS you can see from the responses the answer is clear as mud.

Boiling takes too much fuel.

I'd rather filter for the large particles AND then treat with Aqua Mira.

Yes, I agree. It also takes a very long time for the water to cool enough to be drinkable or appetizing. I filter and/or use pills by default, and only boil water if I'm cooking with it. No troubles with this method so far... knock on wood.

Years ago when I was still sorta of a newbie, I was at a lake that had brown water, thinking it was bad, I proceeded to boil it for ten minutes, over a woodfire. If I ever have to do that again, I will hike to the next lake. I like my smoke flavoring on my meat, not in my water. Yuck!

Yellowstone has a bunch of hot springs with varying temperatures and varying colors in the background. Many of these colors come from bacteria, we were surprised to learn. The clear pool, we heard, was more or less bacteria-free, because it was hotter. The magic nuber for pathogenic bacteria to be killed off was 180 F.

I'm thinking virii and bacteria should be pretty much done it before water gets to a rolling boil, BUT, nasties like Giardia cysts, can take longer. Spore coats on some beasties are why autoclaves became popular. These coatings are very tough and hard to breach.

CM

this about corresponds with what I learned in microbiology class. basically a minute at 65 centigrade, and everyting was toast. The statement of "bring the water to a roiling boil" is because that can be done at any altitide with no tool other than a container and fire. whereas 65 C requires an accurate thermometer at sea level. boiling it doesn't require measuring.

There are two standards that you should already be familiar with. Sterilization is the killing of ALL pathogens, and takes place at temperatures above boiling water for a number of minutes (why you can't do home bottling or canning without a pressure cooker). Pastuerization kills MOST of the pathogens by heating at or above 161F for a few seconds.

At boiling water temperatures, you can't kill everything. But the idea is that you kill almost everything and what's left is in small enough quantities that your body's immune system will handle it without symptoms appearing. Assuming that we are dealing with relatively pure water (you didn't get it from a cesspool), a trip to the boiling point should be sufficient. Actually, just taking it above 161F is sufficient to kill the majority of bugs, but seeing the water boil ensures it's above 161F without carrying around a thermometer.

(Added info) Here's an REI article that says:

Just use chlorine dioxide tablets from Katadyn. Wait 1-2 hours in cold temps, 1/2 hour at summer temps. It kills ALL pathogens and doesn't impart a bad taste, unlike bleach chlorine and iodine.

But, I confess, I boil untreated water for 30 seconds and then use the water for freezer bag cooking, etc. Never got sick... yet.

Eric