Out of all the skills to learn, survival water purification is probably the most important. You can survive for a couple of weeks without eating anything, but your body will start to struggle after only two days without water. The biggest concern regarding water is that in a TEOTWAWKI event, clean running water may be incredibly hard to find. Having the tools and the knowledge of different purification techniques may be the difference between life and death for your family.
Boiling is by far one of the most effective and easiest water purification process to use. Raising the water temperature to boiling point kills off any enzymes or bacteria that may be present in the water, and while you may have to strain the water to get rid of any visible debris, boiling it will purify.
The main downside to boiling as a survival water purification method is that you need a reliable heat source and a container. You'll also have to consider that the more water that you have, the longer you will need to have a fire running. You also need to bear in mind evaporation, which will cause you to lose a certain percentage of any water that you collect.
Adding purification tablets to water is another survival water purification technique. These tablets generally contain high levels of iodine, which will immediately kill off bacteria in the water making it safe to drink.
You may find that with higher iodine concentrations, the water may turn a slight yellow color but it will still be safe to drink. The tablets are obviously one use only, and typical purify around one quart of water. You will need to have a big supply and have a plan of how to get clean water once they run out.
Water purifiers generally come in the form of filters that will fit over the top of bottles and containers. You simply pour the contaminated water through the purifier and clean water will come out the other side. You will need to read the labels carefully about how small the gaps in the filters are, as some cheaper models will not block all the bacteria.
The main drawback with purifiers is that they will clog after a while with bacteria that are invisible to the human eye. This means that it will either take longer for the water to come through or the purifier will degrade and let more contaminants through. They are also a time limited survival water purification system, so be ready to find a long-term solution.
Solar distillation is a late stage water purification system, which assumes you have set up a base camp somewhere and have access to numerous materials. First, you dig a hole, perhaps 3 foot by 3' foot by 2 foot deep, then place a container like a cooking pot in the bottom of the hole. Next, cover the hole with a plastic sheet and anchor to the ground by placing rocks on the edges of the plastic. Leave some give in the plastic; don't make it real taut.
Next, drop a small pebble in the center of the plastic, so that the plastic dips down directly over the pot inside the hole. The sun will pull moisture from the group and evaporate the water, which will then condense onto the plastic sheet and run off into the container below the pebble.
This method will work even in the desert. You can speed up the process by even urinating on the ground around the container. The water acquired through solar distillation is pure water and free of bacteria.
Alongside boiling, SODIS or solar disinfection is a very effective long-term survival water purification system. You need clear plastic or glass containers, like a 2 liter soda bottle, which you fill with water that has been filtered to remove debris. Then you lay the bottle on a piece of corrugate metal, like a metal roof, and let the sun go to work. In eight hours, the UV rays in the sunlight will have killed off the bacteria, leaving you with clean drinking water.
The obvious problem is in the case of an apocalyptic event the clouds cover the sun for days on end. UV light will still come through but very weakly, so it may take days before the water is safe enough to drink, however, you can go off and do other jobs while the sun works its magic.
The one consistent feature of all successful survival plans is to have a survival water purification method or methods. The most effective means of providing water to you and yours is to plan to use multiple methods during the duration of the catastrophic event.