We built a simple, fast tool that traces how much each source contributes to the water quality at the drinking water intake and how long that water stays in the lake/reservoir. It avoids heavy, 3-D computer models and instead uses flow, storage and water quality information utilities already collect.

In Virginia’s Occoquan Reservoir, our predictions captured the familiar seasonal swings and showed where action matters most: winter salt surges are driven largely by road-salt runoff carried in by rivers and streams, while summer nitrogen levels are most influenced by the upstream reclaimed-water discharge.

Because the tool runs quickly, water managers can try “what if” scenarios—like reducing source specific pollutants—and see likely outcomes before acting. This helps communities choose targeted, cost-effective steps to protect drinking-water quality.