Roofs are a great source for rainwater. Rain barrels easily collect water at downspouts where water naturally runs and simple filters (or more elaborate scrubbers) keep debris out. The grey water outputs of showers & tubs can be readily collected by design in new construction and to some extent by retrofitting existing construction.
Today there are many rain water containers on the market, some holding up to 500 gallons: concrete vaults, PVC or vinyl tanks, EPDM-lined reservoirs & more, like in the FALCON at SMV; a water collection system will have two rain-water reservoirs consisting of insulated concrete forms (ICF) walls, compacted gravel floors with underlayment, seamless EPDM rubber lining and a polyvinyl cover.
Grey water can be stored in 500 gallon tanks (underground, insulated with provisions for regular emptying). Ponds are a cheap way to store rain and run-off water.
Rain water is great for use in showers & tubs, clothing & dishwashers, gardens etc. It’s naturally soft; great for washing skin and hair. Grey water is a good for use in toilet tanks & subsurface irrigation. Ponds are useful as an oasis of comfort, an inviting place for wildlife and irrigation in times of rain shortage. Larger ponds are invaluable as a firefighting resource (and their proximity can lower insurance rates).
The important Green Note is this:
we don’t really consume water! We use it then pass it on to other uses & other places.
Water is the ultimate recyclable!