Where I live in San Diego, I have a 2200 sq. ft. roof that I estimate collects around 5-6000 gallons of water a year. I have 1100 gallons of storage. Given enough storage, there is no reason why I cannot run my garden all year on rainwater. It’s amazing to me that every house isn’t collecting rainwater, particularly in drought conditions.
One cost saving way to collect rain is by using IBC Totes (food grade, shown above). These cost under $100 each where I live, and the city also offers credits to help pay for the cost.
If you get these tanks, I suggest you get at least two – you’ll want to put on on top of the other so that you get a bit of water pressure. Elevating it on top of another tank, should give you around 1.6 psi – just enough to get water to fill your wicking beds and run drippers.
When your top tank runs out, you’ll want to fill it with the bottom one. For this, you’ll need a water pump. I suggest using a 12 volt pump so that you can use it with a solar charging battery. This way, you can run the whole thing on the sun.