Just found this amazing set-up for sale! So I have a big garden and I am researching how to better water my garden with rainwater, which I currently do but it is labor intensive and requires an hour a night with a watering can, I came accross this really cool website/you tube videos about a rainwater and graywater irrigation dripperhose system that requires no electricity/no power/very little elevation difference and waters gardens using the exact same amount of water beside the house as 150 feet away. I don't know from experience yet, I have to figure placement (I am going to buy half a dozen of them) and I live in Canada so everything here is still under snow but I thought to myself that this system is exactly what many people need and that I should pass along the great idea to others. The graywater systems look permaculturally good too.
Anyhow, just passing along my research! http://www.besthomewatersavers.com/

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I would think that if you are going to filter the water, which you will need to do for a dripper system, then you will need a pump which will need electricity. I harvest rainwater and use a bubbler system which is less precise but does not often clog and does not need a filter. I do use a pump to pump the water from the collection tanks to the elevated gravity feed tank from which the rainwater irrigates my crops. To fill a 285 gal feed tank takes less than 15 minutes of pumping so electrical power use is minimal. I bought the tanks online and the irrigation pieces at the two big DIY chains and cost was reasonable. Take a look at my website if you are interested.