Which of the following precautions should be taken to protect water supplies during pesticide mixing and loading?

Filling equipment away from any water sources is crucial for protecting water supplies during pesticide mixing and loading. This precaution minimizes the risk of accidental contamination of water bodies, such as streams, rivers, or lakes, that may be nearby. If pesticide residues were to spill or run off during this process, they could enter these water supplies, potentially causing harm to aquatic life, drinking water sources, and overall ecosystem health.

The other options present practices that could lead to increased risks. For instance, using a non-pesticide liquid for mixing does not necessarily address the potential for pesticide contamination at the mixing site. Mixing indoors may help contain spills but does not eliminate the risk of contamination if there are leaky containers or improper disposal of pesticides. Dumping excess mixture in the ground poses a high risk of leaching into groundwater or soil, which can severely impact local ecosystems and water quality. Therefore, the safest and most effective measure is to always conduct mixing and loading activities away from water supplies.