An interesting fact, especially for those of us in low-rain areas: An inch of pH neutral, nutrient-freeing, perfect rain falling on one acre of land is the equivelent of 27,154 gallons of water. Yep. Where does it go? For most people, it runs off into the storm drains and eventually to the ocean where it becomes salty and unusable without treatment. Then a couple of weeks later, on come the sprinklers delivering not-so-good quality expensive domestic water, further locking up the nutrients and killing the microbes in the soil. How can you capture that wonderful resource of natural rainwater? Water barrels are alittle help, but mostly what you need to do is shape your soil to catch the runoff. Swales, deep loam, and strategic planting can quickly take all that water… even the amount that pours off of your roof, and capture it in the soil. The water slowly sinks and moves the way it was going before, but without taking the topsoil with it. As it moves, the plant roots absorb it over a long period of time, along with all the nutrients that pH-neutral rainwater has freed up in the soil. Your landscape will be stunning, your water bill can eventually be reduced to zero, and if you grow food plants, the nutrition level in them will rise. Here is a video from permaculturalist Geoff Lawton with graphics: http://www.youtube.com/watch?v=UFeylOa_S4c.
This is the essence of permaculture. Simple, logical effort to use what we already have to return the soil to the sponge it was before we compacted it. So how large is your plot of land? Nine acres? A back porch with pots? You can still do the math and see how much water you can capture. Look up rainwater harvesting videos on YouTube and see plots of land in the desert that harvest rainwater and are oasises of food, habitat and beauty, without supplemental water. Here is what Lawton has done with ten acres in Jordan: http://www.youtube.com/watch?v=xvmx4lcqQVw. If they can do it on that scale in that poor an area, any homeowner can do it.