How can an applicator best protect a water source at the pesticide mixing site?

Using backflow prevention devices is essential for protecting water sources at a pesticide mixing site. These devices are designed to prevent contaminated water from flowing back into the clean water supply, thereby ensuring that any pesticides or other chemicals used do not enter wells, rivers, or other water sources unintentionally. This is particularly important in areas where pesticides are mixed or handled, as there is a risk of spills or splashes that could lead to contamination.

In contrast, mixing in well-drained areas might help in managing runoff but does not directly address the risk of backflow, which is a more significant concern for water source contamination. Submerging the filling hose could potentially lead to contamination if the hose is submerged in a contaminated tank, making it an unsafe practice. Mixing on a containment pad is a good practice for handling spills but does not specifically prevent backflow into water systems. Therefore, using backflow prevention devices is the most direct and effective method for protecting water sources from pesticide mixing activities.