Martin Lester, of Portsmouth, England, asks :-
Surface tension draws water up a tube. Could a very large number of very fine tubes be used to draw water to the top of a water tower and use this water to generate power?
David Painter, a natural resources engineer at the University of Canterbury, New Zealand, responded.
It is simplest to think of just one tube. The explanation applies to as many tubes at once as you like. There is no problem, in principle, in allowing surface tension at a suitable liquid-solid interface, such as water-glass, to lift water up the tube. The hollow top surface (called the meniscus) gives an upward force that lifts water until the weight of lifted water just equals the surface tension force. So the lifted water has "potential" energy through being elevated above its original place. If you arrange for it to fall back there, you could run a turbine or other energy-generating device on its way.
The problem is: how are you going to persuade the water to leave the tube while surface tension is still holding it there? Unless you change the surface tension (add a little detergent?) you still have to overcome this force to remove the water.
Any way you can think of to get the water out of the tube will require providing energy, either stored as in a chemical to alter the surface tension, or the energy of some force moving through a distance (doing work).
Not only does the first "law" of thermodynamics tell us that you will not be able to get more energy out than you put in, the second "law" of thermodynamics tells us that you are not even able to retrieve that much, some energy always being lost in real processes.