The article introduces a new method to estimate how much rainwater seeps into the ground on hillslopes. By studying water flow in a hilly area in California, the researchers found that the type of rock and plants in the area affect how much water gets stored in the ground. They discovered that rainwater first fills up the ground near streams before moving uphill, increasing the amount of water that recharges the groundwater as the wet season progresses. This study helps us understand better how water moves through hillslopes and into the ground, an important part of the water cycle.