Which of the following statements is true regarding surface and groundwater?

The statement that both options A and C are true reflects a comprehensive understanding of the management of surface and groundwater.

Considering the first part, surface water, such as lakes and rivers, can be heavily influenced by pollution from urban runoff, agricultural activities, and waste discharges. Therefore, it is essential to treat all surface water as potentially unsanitary unless it undergoes proper purification processes to mitigate any contaminants. This reflects a cautious approach to safeguarding public health.

On the other hand, the second part emphasizes the importance of surveying the entire watershed for surfaces water supplies. A watershed is the land area that drains into a specific water body, and understanding its characteristics—such as land use, potential pollution sources, and ecosystem health—is crucial for determining the quality and safety of the water supply. Comprehensive surveys are necessary to develop effective management strategies that protect water quality.

Thus, the combination of these two considerations encapsulated in the answer underscores the critical points about water quality and source management in the context of public health and environmental safety.