New York City's water supply system is one of the oldest and most complex in the nation, delivering more than 1.1 billion gallons of drinking water each day from three upstate watersheds, serving over 9 million people in the City and its surrounding counties. In response to evolving permitting requirements and storm events, the City developed the Operations Support Tool (OST), a computer model that incorporates data on dozens of variables to help water managers optimize timing and volume of water releases. The NASEM will review the City’s use of OST for managing turbidity as well as many other objectives.