Collecting rain water from rooftops is a simple and sustainable way of gathering water that can also help soil and water quality by reducing erosion and runoff.
Many buildings are already fitted with gutters that are sufficient for rainwater catchment and all that's required is the installation of one or more collection tanks (a 50 gallon drum can be a good start for home garden use) and pipes diverting downspouts to tanks.
Using rainwater for irrigation
In most cases rainwater collected from roofs in can be used directly on gardens during dry weather.
Using rainwater drinking
Depending on local air quality rainwater may need to be settled/or purified before drinking.