Gary Kurtz estimates that using water instead of petroleum fluids in hydraulic systems could save 500 million gallons of gasoline in the U.S. alone. Saving fuel is one reason the professor of agricultural engineering and his students at Purdue University built a lawn mower that is propelled and steered with a water hydraulic system. They are demonstrating that water's lower viscosity boosts the mower's energy efficiency. They also hope to show that the technology may be practical for agricultural, construction, mining, and forestry equipment. Viscosity is a measure of how fast liquids flow. Water's lower viscosity means less energy is required to push it through the system. Kurtz estimates that the cost of building a water hydraulic system for his mower is approximately twice that of a comparable petroleum-based system. However, he points out that the costs of stainless steels and ceramics needed for making water hydraulic systems are dropping, "We have a proposal in to a golf course association now," says Kurtz. "They like the idea because oil leaking from the hydraulic systems in lawnmowers kills the grass on golf course greens." Danfoss, Fairchild Manufacturing, Indianapolis Valve and Fitting, Parker-Hannifin, and Swagelok provide equipment for the project. Jacobson, a division of Textron, donated the mower retrofitted with the water hydraulic system. For more information send e-mail to Kurtz at firstname.lastname@example.org.