Yeah, it's just tap water from my kitchen sink. It's in 1 gallon clear bottled-water bottles (Crystal Geyser). The bottled water tastes a bit better than my city tap water so I used to buy the bottles for drinking and rather than throw out the empties, I'd refill them from the tap and store them just in case. I do have some bleach and purification pills around and I supposed I'd use them if I were to need to drink this old saved water (maybe 8 gallons or so under the sink). I'm in a small apartment in an urban area, no space for a 55 gallon drum and I figure I'd go without creature comforts like showers for a few days if something bad happened here. I sometimes think of getting an Aquaflex flexible tank (60 or 110 gallon) and putting it under my bed. It's sort of like an inflatable air mattress (3x6 feet by 5 inches or so for the 110 gallon model) with garden hose fittings to fill it with water. See http://www.aquaflex.net for info. The 60 gallon one could possibly be transported full in my small hatchback car if the need arose.

Note that the cost of most water containers is ridiculous; it's cheaper to just buy actual bottled water (those 1 gallon bottles are 1.29 each at the corner grocery and they have sturdy screw caps, not the pop-off type). I found an online source of food grade polyethylene garbage bags so if I wanted to store water in large volume and didn't use Aquaflex, I'd possibly use normal 20 or 33 gallon PVC garbage cans lined with those food grade PE liners.

Finally, I live near the ocean so there's infinite salt water available. I sometimes kick around the idea of getting an RO desalinator on ebay, but they're on the expensive side.