Following up on what Arbilad and Poltax said...
They should definitely be off the ground, they need to have peroxide or bleach added, (even if your city water already has chlorine in it), and they really need to be shaded to slow the process of the plastic becoming brittle from age and exposure to the sun.
We used 55 gallon drums (the white ones, but blue are fine too, but if you open the white ones to see if the water has algae growth, light comes through the white drums very well and allows you to "inspect" the water much more easily), and we stored them in our garage. Started by adding 1/3 cup of bleach and then the water (regular bleach, not one of the scented ones) and drained and refilled them every 2 years. Never had a problem. And although the sun never saw them, the temps in our garage were much higher than sitting outside would have been
If you're getting second hand drums, you need to know what they were originally used for... They must be food grade, and never have had any chemicals stored in them.
As Arbilad already pointed out, they will absorb whatever was initially in them and it will bleed back out into the water.
Our 10 drums came from Pepsi, and were initially used for the syrup they use for making Pepsi Cola.
We have wooden stands that hold 2 drums each, one above the other, and the drums lay on their side with the bottom drum being about 8" off the ground and the upper drum being about 6" above the lower one.
The upper bung is sealed (with teflon tape) and the lower bung has the center knocked out with a typical brass faucet threaded in (also using teflon tape), so getting water is a breeze.
Because the bungs are typically 3" from the edge of the drum, the lower bung/faucet is about 11" off the ground, so plenty of room for a pitcher or bowl or whatever you want for getting water. Also, we drill a 1" hole in the side of the drum, just 4 or 5 inches below one of the bung holes (so when the drum is turned on it's side, spin the drum so that bung hole is at the top and then the hole you drilled is now on the very top). Now you can use that hole for filling the drum, so you can fill the entire thing, instead of just to where the upper bung is located (which is not nearly high enough, when the drum is laying on its side). When you're at the hardware store buying the 1" drill bit, you can also buy 1" plastic plugs to cap the drilled hole... it all works out great.
The much larger totes (which will hold between 275 to 330 gallons) are great, but tend to be much more expensive, much harder to find in "food grade" (ei, they weren't used for some unknown chemical), and can not be moved once filled.
My drums (with 2 to each rack) can not be moved, once filled, either, but if your drums are individual, 4 guys can lift one into the back of a pickup without too much difficulty.