Early settlers in the town of Dry Gulch drilled wells to pump as much water as they wanted from the single aquifer beneath the town. (An aquifer is an underground body of water.) As more people settled in Dry Gulch, the aquifer level fell and new wells had to be drilled deeper at higher cost. The residents of Dry Gulch will overuse water relative to the social optimum because:. a. each resident will fail to adequately consider the external cost of his or her own water use
b. water is a scarce resource
c. each resident will fail to adequately consider the external benefit of his or her own water use
d. the marginal cost of water is increasing

Dry Gulch Town

The residents of Dry Gulch will overuse water relative to the social optimum because:

a. each resident will fail to adequately consider the external cost of his or her own water use

Explanation:

When individual households in Dry Gulch dig their own wells, each household will usually overuse the water because they are not paying any incremental costs except for the maintenance of the well.  Again, the aquifer level around the area usually falls due to overuse and this makes it difficult for new residents to find water unless they dig deeper wells at higher costs.   So, there is always some social costs (sometimes immediately external to the households) for individual households to dig their own water wells instead of community or commercial wells that will help regulate water use.