Zach Klein wrote a great article on how they made a 800 square feet garden in San Francisco's Mission District:
This garden was conceived to help expand San Francisco's urban forest and it was designed to be an example of xeriscaping. It is drought-tolerant and requires no additional water other than seasonal rain. It is also a permeable landscape that improves the city's sewage treatment capacity by reducing storm water runoff through absorption.
Look at how beautiful it is:
I would have never guessed it's in the SF Mission district: