New York City's water supply system is one of the most extensive municipal water systems in the world. This complex system relies on a combination of tunnels, aqueducts, and reservoirs to meet the daily needs of the city's over 8 million residents and its many visitors. Thanks to well-protected wilderness watersheds, New York's water treatment process is simpler than in other American cities. One advantage of the system is that 95% of the total water supply is supplied by gravity. The other 5% needs to be pumped to maintain pressure, but this is sometimes increased in times of drought when the reservoirs are at lower than normal levels.