New York's water treatment process is simpler than most other American cities. This largely reflects how well-protected its watersheds are. The city has sought to restrict development surrounding them. One of its largest watershed protection programs is the Land Acquisition Program, under which the New York City Department of Environmental Protection (DEP) has purchased or protected, through conservation easement, over 130,000 acres (53,000 ha) since 1997. With all the care given, the city's water supply system is exempted from filtration requirements by both the federal and the state government, saving more than "$10 billion to build a massive filtration plant, and at least another $100 million annually on its operation". Moreover, the special topography the waterways run on allows 95% of the system's water to be supplied by gravity. The percentage of pumped water does change when the water level in the reservoirs is out of the normal range.