Since the beginning of recorded time, mankind has been using collections systems to gather and store rain water for future use, and while the appearance of the systems has changed, the basic elements that make them up have not. All you need is a wide surface and a piping system to direct the water to the storage device.
Roofs and down spouts fulfill the first two requirements and are at the disposal of every homeowner, it’s getting a proper water storage device that trips up most would be water collectors.
Follow the photo-link to read detailed, step-by-step instructions for building your own "perfect rain barrel system".
Talks about a way to make a easy watering system for your garden.