This is not quite as complicated. Here I am speaking only about reusing rainwater on a small scale. Rainwater can be collected and redistributed to your garden very simply. Instead of letting rainwater run from the gutters into the street and into the city storm water system, it can be gathered in rain barrels and used when most needed.
Here are some places for learning about how to make your own rain barrels:
As you can see from the plans a spout is attached to the base to attach a hose and make watering easy.
Another fun water use for the garden:
A bird bath!