Probably a stupid car question...

[kandrathe]

Unfortunately, that won't work. You'd still need the powered pumps to draw the water out of the 'uphill' end of the capillaries, and that would cost more energy then simply pumping the water up.

There is no perpetual motion here, so yes, you'd probably still need some smaller "pump" to over come the positive flow velocity dictated by Hagen-Poiseuille. Nature accomplishes its "pump" by using solar energy to evaporate the water in leaves.

I also believe you could achieve some flow effect by transforming the shape of the pipes at the top. Have you ever heard of a Hydraulic Ram?