Rain water harvesting or collection has been around for thousands of years.  Rain water harvesting is basically collecting the rain that falls typically on a roof and channeling it into a containment system.  The rain is stored in tanks and then can be used for household consumption as potable water or as non-potable water for use around the house or on your property.

Rain water is the purest type of water that you can use and doesn't contain harmful chemicals or contaminants.