In the past, public interest criteria were met if the licence applicant could derive an economic benefit from the use of water. More recently, public interest criteria have been extended to environmental and other public concerns, requiring consideration of the cumulative effects of abstraction from groundwater or surface water. Similar protections include state laws that set minimum throughput requirements or approve inflows. Municipal water suppliers are all Group A municipal water systems with 15 or more residential connections and Group A non-municipal systems that provide water for residential purposes (e.g., bathing, cooking and cleaning) to a non-resident population for 25 or more people 60 or more days per year. The doctrine of public trust is a common law doctrine rooted in Roman law, which states that certain natural resources, such as navigable waters, are permanently preserved for the benefit of the public. The State acts as trustee of the common resource and is obliged to manage it in the interests of present and future generations. Attempts by a state to limit or eliminate the rights of the public trust through sale or other means may be found to be invalid. The consumption of uses modifies the water cycle and can change the environment. Because the same drop (or even molecule) of water can be reused multiple times by humans and is also needed to maintain environmental integrity, conflicts between different uses are common. Water law seeks to resolve these conflicts by encouraging desirable uses and discouraging undesirable uses.
Uses are encouraged or discouraged by the complex interconnection of water rights systems and the exercise of state power. Groundwater allocation systems often distinguish between on-land and out-of-area uses. Leaflet use is when water is used on the leaflet where the pump is located. Off-field use is where water is transferred to another location for use. The priority date is the date on which the reservation is made. Private rights established prior to booking prevail over reserved rights. Federal law cannot be abandoned or lost by non-use. Once invoked, it may draw water from private rights holders whose rights have been established under the reserved right. In addition, water rights are rarely exclusive.
This need to share water leads to conflicts between individuals with private rights, between individuals with private rights and people with public rights, and between those with federal rights and those with state rights. Water law is used to resolve disputes between different plaintiffs by determining the rights and obligations of each party in a lawsuit. Traditionally, water resources management has focused on surface water or groundwater as if they were separate entities. Although water is part of a connected system, it tends to be regulated according to its source. Even within the surface water category, water regulation can vary depending on whether the surface water is perennial, volatile or artificial. To have a valid allocation, an appropriator must demonstrate the necessary intention to make an allocation. The necessary intention is usually only the intention to divert the water and apply the water for a useful use. In States that require authorization, the application for authorization shows objective evidence of the required intention. A priority date or the date of first water use is assigned to a valid allocation. Some States have developed the doctrine of regression, which allows the appropriator to use the date on which the intention was formed as the priority date. The doctrine of correlative rights allocates water on an equitable basis among landowners and allows off-parcel uses, although these uses are contingent on uses on parcels.
Like the absolute dominion rule, the doctrine of correlative rights determines groundwater rights based on land ownership. The difference, however, is that landowners above the same aquifer are limited to a fair share of the total aquifer supply, rather than having an absolute right to groundwater or unlimited rights to pumps. Under the absolute dominion rule, also known as the “absolute property rule” or the “English rule,” a landowner is allowed to use as much groundwater as possible. The rule does not take into account any impact on neighboring users, so an owner could monopolize the entire aquifer without becoming liable. This doctrine creates an incentive to pump as much water as possible, as it is not about suffering penalties from a neighboring user.