An example of a surface water supply would be which of the following?

The correct response is a reservoir, as it exemplifies a surface water supply. Surface water supplies are bodies of water that are open to the atmosphere and include lakes, rivers, and reservoirs. Reservoirs are specifically designed to hold and store large quantities of surface water, which can be used for various purposes, such as drinking water, irrigation, and recreational activities. They collect water from rainfall or runoff and provide a controlled environment where the water quality can be monitored and managed.

In contrast, sources like a well, a rock and sand spring, and an earth spring are categorized as groundwater supplies. These sources rely on water found beneath the earth's surface, which is accessed through drilling or natural springs. The distinction between surface water and groundwater is essential in environmental health and water resource management, highlighting why a reservoir is the exemplary answer in this context.