Pumping water was one of the first and most important uses for windmills. That, and using the energy for turning a millstone to grind grain is also important. These days, windmills are used mostly for the generation of electricity but you may still find some old ones grinding grain or pumping water. There's one in a park just south of the University of Illinois here that pumps water.
A water pump operates on reciprocating motion -- up and down pushing and pulling on a piston which draws water up out of the well. In addition, there is a one-way valve to keep the water from flowing back into the well when the pump makes a return stroke.
A windmill generates rotary motion by turning a shaft. The speed of the turning can be adjusted by using gears of different sizes. To turn the rotary motion of a shaft into reciprocating motion, a crank is used. A shaft or wheel is attached perpendicular to the turning shaft, and another rod is attached vertically from the edge of the wheel to the pump down below. Because the center of the wheel does not move but the edge goes round and round, the rod will be pulled up and down (and a little bit to the side and back each time, so you'll need a hinge when connecting the rod to the water pump's piston). There should be some way to disengage the gears and rods so that you can shut the pump off when you want to.
These days, you can generate electricity with a windmill and connect that to an electric water pump. There are always losses of energy in each conversion step however. An electric pump will offer more conveniences of being able to speed it up or slow it down, or to use electricity from the power company when the wind isn't blowing.
(published on 10/22/2007)