My last real post was on depletables, so I figured I should continue on that theme with the topic of water. As I said in the Depletables post, the two depletables you cannot avoid are food and water. Water especially, because you will not survive three days without water. Now, based on your situation, there may be a greater or lesser availability of water. Despite that, however, having sufficient water must remain a top priority.
The first thing to keep in mind is if you intend to be stationary or nomadic. In terms of water availability, being stationary would simplify things, simply because you could base yourself around where the water is. Being nomadic, you would have to constantly be aware of where your last water source was, how much water you have left, and where your next source of water could be. However, being nomadic you could also more easily adapt should your current water source be depleted. Each option has its gives and takes.
I intended for this blog to have unconventional suggestions for unconventional situations. Collecting water in traditional survival environments (woodlands, wetlands, tundra, etc) is something covered pretty well in traditional survival guides, so I will not repeat that wisdom here. There is one environment, however, on which I would like to comment: the urban setting.
The first thing you should do is find everything that can hold water. After that, proceed to fill all of them from hoses, faucets, etc... It is unclear how much longer the water will be there, and it's the cleanest water you're going to find, so I would recommend capitalizing on as much of it as you can. Do not wait until this water has run out before you search for a different source; stay a step ahead. However, depending on your apocalypse and the level of decay in the urban area, a non-pure urban water source could be as, if not more, dangerous as natural water sources. If there is any apparent risk of there being man-made contaminants in the water, avoid it; it is not worth the risk on your life. If the water seems to be contaminant-free, you still need to purify it. You could use the traditional methods of boiling, filtering, or using water purification tablets, but there are a few methods which could be more available in an urban setting.
Bleach: Using bleach to purify water for drinking is a method that comes highly regarded. Clorox distributes bleach during disaster relief for this purpose. 8 drops to the gallon is sufficient to kill any malignant bacteria that may be lurking in your water. That is quite a small amount of bleach, considering that it's sold in massive quantities. Furthermore, I don't think one would be hard-pressed to scavenge bleach in an urban setting. However, bleach loses its strength over time, so after a while you'll need another purifier.
Alcohol: In ancient Greece, they didn't drink wine for the sole purpose of getting intoxicated. Someone really early on noticed that when people drank water they would sometimes die, but if they drank wine, even if it was mixed in with the water, they would not. Thus, wine became their staple beverage. There is no shortage of alcohol in cities, and it does not lose strength over time, so pouring even a small amount of wine into your water will go a long way in protecting you.