Rain has been used for thousands of years as a source of water in large parts of the world, but in modern society, it is not as common as it once was.
There are however some that have started looking at the possible use of collected rain-water in their homes. It is common among those that are looking into ways of living “off the grid” but it can also be implemented as part of an energy-saving plan for a home.
The concept is very simple – rainwater is collected in some manner off of a large surface and then funneled into a storage location. Your implementation can vary a lot depending on what you are planning to use the water for, however.
For example, if you are just planning on collecting water for use in watering your garden or even to flush a toilet, then you could just use a barrel underneath a downspout coming off of your roof, but if you are planning on doing other things, like use it for cooking, shower or even drinking, you need to consider both the surface you are collecting the water off of, as well as a filtration system.