To study the flow rates and flow paths of underground water, scientists placed non-toxic dye in caves and sinkholes throughout the recharge zone. They put receptors in various wells and springs throughout the area to detect the dye. They found that water flows through its underground passages suprisingly quickly. For example, water traveled the nearly twenty miles from Onion Creek near Buda to Barton Springs in as little as three days. Travel times from other dye traces are noted on the map below. Most water re-emerged at the four Barton Springs outlets, but some pathways in the aquifer flowed to Cold Springs on Town Lake. On average, more than 32 million gallons of water a day resurfaces from the aquifer at Barton Springs.