Imagine if instead of every building having parking spaces, we required a mandatory water store and used that non-potable water for watering green spaces, flush

Imagine if instead of every building having parking spaces, we required a mandatory water store and used that non-potable water for watering green spaces, flushing toilets, etc. Doesn't remove the impact of agriculture but it does make residential areas more resilient in times of draught. But that would require public transit and California is rather lacking in that regard. Even LAs plan for metro expansion is going to take 30-40 years.