A healthy adult can last a week or more without food, but only a couple of days without water. In a disaster water supplies may be contaminated or just plain unavailable. Thus, if you put nothing else in your Go Bag ensure you have some water.
Depending on size, amount of exercise and climate the average adult will need to drink 2-4 litres of water a day. You can calculate what your needs might be here. Add a little extra for sanitation, multiply it by a few days and your talking about 15 litres, per bag. One litre of water weighs one kilogram so your Go Bag could get pretty heavy if you carry all the water you need fresh.
However all these treatment methods below depend on you finding water, which may or may not be easy. I recommend you carry as much clean water in your Go Bag as you can.
There’s a range of different ways to carry fresh water. You can buy it bottled or use containers (including ‘Camel-back’ type bladders). Remember to periodically change the water, particularly if you’re using your own bottles.
I prefer one litre clear plastic bottles. It means your supply is split up (in case one of the bottles breaks or is contaminated) and once you’ve finished a bottle, you can use the empty to start purifying any water you find straight away.
As you can’t carry enough water to sustain you for more than a couple of days the answer is purification. There’s a variety of methods you can use, but regardless of your choice you should always try and purify the freshest water you can find.
One pitfall of purification is that although most methods will kill all micro-organisms in the water, they generally can’t remove any chemical contamination such as pollutants.
All these methods are less effective (including the filters, which are designed for small particles including bacteria) if the water you find has lots of dirt or other matter in it. You should try and use some sort of coarse filter (or you can make an effective filter using sand, material and a funnel) to remove most of the gunk before proceeding.
Boiling water is the tried and true method of killing germs, including viruses and parasites. However it’s dependent on having a container to boil the water in (though I have seen water boiled in a plastic bottle) and enough fuel to light a fire. Don’t depend on this method.
A mainstay of stationary disaster water purification systems there are also portable filters that will remove all micro-organisms from water (though beware, most cheaper filters won’t). The advantage of some filters is that they can also remove certain pollutants and other contamination. The disadvantage of filters is that they can be expensive, bulky, clog easily and once they’re broke are difficult or impossible to fix. If you choose to carry one in your go bag don’t forget to back it up with something else.
You can buy filters at most camping and trekking supply stores.
The two prevailing chemical treatments are chlorine and iodine. There’s not a huge difference between the two (though there’s plenty of arguments on the interwebz about which is the superior treatment), but keep in mind that some people can be allergic to iodine. There’s a variety of different formulations out there, just follow the instructions on the container. I like chemicals cause they’re cheap, lightweight and can purify a lot of water.
Depending on where you are you can purchase these products at chemists/drugists, camping stores and supermarkets.
There are also UV sterilisers on the market as well as other chemical products which use silver. UV sterilisers use precious batteries and silver treatments are not widely available but depending on your situation may be worth investigating.
Alternatively if you’re out of options a clear (PET) plastic bottle filled with shaken water left out in the sun for around 6 hours should kill most microbes.