I just checked out the brute commercial 35 (or was it 30 or 33 gal) garbage cans at lowes and home depot. imo, it will not hold up to the weight of 30 gallons of water and will "beer belly" out, like mentioned above. now you may be able to put a ratchet strap from the top 1/4 of the can to help support the weight of the water, but don't quote me on it.
off to menards to see if they have a rain barrel.
back when I was a chef for many many years (15 years ago mind you), we used the grey brute 35 gal trash cans to hold our lettuce (salad). so +2 on them being food safe.
craigslist has an abundance of food grade "rain barell" type of drums. most say they were used for food processing of banana peppers or pickling with vinegar. anyone know if a thorough bleach then hydrogen peroxide cleaning will remove the vinegar residual vinegar odor and be safe for water storage? I can find hundreds of these barrels for under 25.00 each.