**2. Some models of groundwater use and the potential for groundwater management**

It is necessary to take into account that implicit in the different concerns about groundwater, an essential principle can be found. This is related to the fact that if no intervention exists, then groundwater pumping will be mismanaged. Another important point that needs to be pointed out is that if groundwater pumping is inefficient, then, the lack of central (and optimal), control, underlines that the estimates of the welfare loss (under the common property regime) should depend on the specific model of firm behavior which might be enlisted in the analysis. This should allow to conclude in favor of an existing potential and pressing need for the development and implementation of management policies for groundwater resources [32].

It is also interesting to point out that when groundwater withdrawals exceed recharge, water will be mined over time until either supplies are exhausted or the marginal cost of pumping additional water should become extremely expensive [33]. An essential issue related to this assumption is that a marginal user cost is associated with mining groundwater, and this is related to the opportunity cost which is connected with the unavailability in the future of any unit of water used in the present.

A well-organized distribution should consider this user cost, which effectively signals the scarcity of the resource and is called the resource's scarcity rents. Therefore, efficient pricing of a resource that exhibits natural supply constraints incorporates both marginal cost of extraction and scarcity rents. Scarcity rents must be imposed on current users.

Given the complexity of establishing clear groundwater property rights, scarcity rents are frequently difficult to be recognized and are not easy to be estimated. Some authors in which a discussion about this point could be found are, for instance [31, 34–37].

 Ignoring scarcity rents implies that the price of groundwater is usually too low and extraction is above the socially optimal level. If an optimal dynamic management of common-pool groundwater resources is not considered, or in the presence of a competitive extraction regime ignoring scarcity rents, results in inefficient pricing and misallocation of resources. This essential argument has to do with the way markets behave, and it could perfectly be competitive. Under these circumstances, the problem is not so much with the market mechanism but with the way property rights behave.
