If your site is flat, build it at the low point of the site. A small pump can be used to pump it up to a storage tank where it can gravity-flow to water your garden. If your site is large or if you own a pair of houses and rent one, with a garden in the middle (the smallest type of house cluster) you may need rain troughs to carry the water to the pool. The Spanish have built rain troughs for centuries. Those at the Alhambra are gorgeous but expensive, but you can build them really inexpensively as well.
Who can do this?
What does it cost?
Who can help?