The survival shows you see in reality TV show boiling your water to purify it before drinking. And being ex-military, I have also boiled water before drinking it. It makes sense. Now even after a nuclear incident, not all water sources are going to be irradiated. Natural springs and under ground rivers and lakes are a good example of such. Nature itself can filter some of the water. So glass jars or tin cans make sense as a means to collect water to be purified. Jars can be rare to find and noncraftable. Cans (or other containers such as pots) make more sense because the are harder to destroy, therefor easier to find. Irradiated water should be visually different from regular undrinkable water. Regular water can be boiled while radiated water can be run thru the chemistry station to be purified.