Thats great, now if we can only get it to rain in July, when the garden needs the water, so we can save it in a barrel. Al

Good going Rhino. My 3 trash cans are full. As Al mentions it is long used up by July. :-(

Great job, sf_rhino!

I save rainwater in trash bins and apply it to the driest parts of the garden within a couple of weeks of the storm. Then I can keep the irrigation system off for an extra week or two or three if no more rain occurs. The good rainwater also helps wash the hard water deposits from the irrigation water to below root level. It does help.

You can also use a hose to siphon water out of the barrel and over to some distant part of the yard. Good if the water would run off into the street otherwise, or just to reduce the amount of water collecting along the house.

Like I said, this is just the start of a larger plan but when I saw the reports of that big storm coming I thought, why waste the opportunity to get started. I figured I wouldn't have enough capacity but I didn't expect the trash cans to fill up before I had had my first coffee.

I had been catching previous light rains in buckets to use on my potted plants.

This is my first year in my house so don't know how great my water usage will be once I get the garden going, but a week or two stored is a week or two not coming out of the reservoir or down the storm drain.

Maths: my roof is about 1250 sq feet and I am collecting from about half of that area which means I have about 390 gallons per inch of rain fall that I could be collecting. I collected 64 gallons and it's rained about 7 inches since I put the cans out... so I've got about 2.5% of what hit that half or my roof. Man, I'm surprised it is so much volume. I was thinking about doing a 250 gallon capacity setup but maybe I should do more.

What do you think is a typical spring/summer weekly usage on a medium-sized suburban garden plus fruit trees?

Are you going to be able to redirect that water down the drain in pic number one, now the barrel is full?

Here are the reference evaporotranspiration (ET0) numbers for SF. They are in inches per month. This shows how much water turf grass (reference plant) requires each month for healthy growth. Now some plants like thyme only need moderate amounts of water so you would calculate a water budget of like 50% ET0.

Let's take a look at July. ET0 is 4.9 inches for the month. For a 1000 sqft lawn, that will require about 3000 gallons of water in the month of July. So of you want to collect water from your roof and store it in a cistern for summer use at maximum ET0, you are probably looking at needing something in the neighborhood of 10,000 gallons.

Or you could do a greywater conversion and have 25 gallons per day per person just from the shower alone. Family of 4 equals about 100 gallons a day for showers. That's about 3000 gallons a month every month.

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I like to recommend this book because it really handles the irrigation issue really well. There is a whole section with examples explaining how to come up with an irrigation budget based on ET. He breaks down the water requirements for plants into very low, low, moderate, and high with what that would mean as a percentage of ET0. He also describes two different watering schedules. The first requires an even amount of water throughout the year and the other has an allowance for reduced summer water. So if a plant is described as M1, it is going to need about 60% ET0 all year long. Other plants might be described M/L2. That means it needs about 60% ET0 during the growing season and about 30% ET0 during summer dormancy. It is a very useful book.

Here is a link that might be useful: Bob Perry book - Landscape Plants for California Gardens

The sentiment is good. But our needs in summer are huge. You could drain a large fish pond in days using a pump to water the garden. And that's for,say, 2,000 gallons of pond.
I myself often think its miraculous that all year we have water based on a few storms in winter.
And,I read that some say saving water that falls on homes and businesses is bad for our aquifers.
No matter what we do we impact the ecosystem I guess.

Thanks for the numbers, nil. I'm a little shocked but that just makes me all the more interested in removing the small bit of lawn that I have. It is only about 200 sq ft, but that still would be a couple thousand gallons over the summer months.

Stan do you have a fish pond? I guess I need to increase my storage capacity by at least an order of magnitude. From what I can tell the majority of the water during a storm seems to be going down the storm drains marked "drains to the bay" so probably diverting the portion from my roof has little effect on aquifers relative to all the non-porous ground cover in the city.

My neighborhood seems to be relatively saturated in terms of ground water anyway. We've got a couple of springs that were flowing even over this past summer. I'm thinking it has something to do with the fact that we are on a slope 200 ft down from the string of reservoirs along the fault line.

Stan, how much do you water your trees? Just over the summer?

I have several small yards divided by home and rental cottages. So,I just use a long hose here and not so long there to water by hand.

One thing about roof water,is that its worth it for some plants that need pure water- like Carnivores or some South African restio seedlings.

I bought Bob Perry's book when first published in 1992 for less than half the price being asked now. This is typically what happens when a book has been selected for a college requirement. No wonder a loan is required to attend a college. Al

I think you might be thiking of a different Perry book, Al. The first edition of the one I mentioned was published in 2010.

You are right nil13. It is Landscape Plants for Western Regions that I have, still a great reference. Al