How to Boil Water For Survival

You would think that boiling water is simple and straightforward.
You grab a pot.
You put water from the tap in the pot.
You put the pot on the stove and crank it to high and wait a few minutes until water is all turbulent and steamy. It will go faster if you put a lid on top, higher partial pressure and all that.
Congratulations you just killed all the germs in that pot of water. You now have safe drinking water. At this point you could even add a flavorant, like my favorite: hot cocoa mix.

This is also known as pasteurization. One of the top 5 health upgrades ever. Good to know if you have a access to a cow or raw milk. And also helpful if you made some stock and going to use it just to be sure, since your average meat stock is low in acid and rich in protein, making it an ideal bacteria breeding ground.

If you are into canning you'll use this to sterilize your jars and tools, and it will also work on medical supplies if there is a long term emergency and you are having to do it yourself.
You can even pour it over dishes and flatware to sterilize them, a useful tip if the dishwasher isn't working and you're sick.

If you are out in the wilderness and can make a fire you can sterilize the water even if you don't have a pot. Water boils at 212°F (100°C) at sea level but only 203°F (95°C) in Denver. Which is a lot lower then the melting point of a lot of materials. You can boil water in a paper cup though the top edge will burn off. Even a plastic water bottle will work, but you'll want to suspend it over the fire with some rope, hot rocks would melt the plastic. The fire will only discolor it. You wouldn't want to do that for the long term, chemicals and stuff, but it would keep you alive until rescue.

This also prepares you for a cooking skill upgrade. Once you can boil water you can learn to poach, braise and simmer foods. But that is another post.