Do you have a garden or just a few plants that may need watering this summer?
Many food processing plants will give away 55 gallon drums that are suitable for rain collection. Clean out thoroughly and place under a downspout. When it rains, your "drum" will be full and ready to use! (or, in the case of having children: to play in!)
Make sure to dump out every now and then to prevent bug problems and/or stagnation.
Linked with Frugal Friday