In the midst of a record breaking, epic drought in California, decisions on water use are being based on an out-of-date and convoluted set of rules. These rules, centered around water diversion rights, are not working. Another tool is available as a drought response tool –— a powerful legal doctrine at the foundation of state water law. Yet it is not being used.

California’s precious water is owned by the State of California, not by individual water users. The latter have property or contractual rights to the use of water based on a complicated set of water-right rules and laws. These laws reflect the history of California.

There is a simpler legal tool that requires all water diverters to ensure their use of water is “reasonable.” Although this basic legal doctrine underpins all our water rights, it is rarely deployed to bring water excess under control.

When California became a state, it adopted the common law of England. The right to use water under the common law was called a riparian right. This “riparian” right was based on ownership of land alongside a water course. As long as the water use was beneficial, the riparian water user could take such water as needed on the land that was “riparian” to the water course.

As California became a state, the gold rush ensued. Soon it became necessary to divert water to mine gold. Since the water was often needed for use on non-riparian lands, a new water right was established to address this circumstance. The “appropriative” water right was established. This right was based on the time water was diverted for storage and/or use on non-riparian lands. Priority was based on the principle of “first in time, first in right.” Eventually. the courts upheld both types of rights.

Most of the major water projects – reservoirs and canals – in California are based on appropriative water rights. Massive projects were constructed to store and convey water from the wetter north to the more arid south. Since these projects were constructed after most land in California passed into private ownership, riparian water rights have priority. They were the senior water rights.

Thus, a priority system developed that led to some untenable situations. In some cases senior riparians, as long as they were diverting water to beneficial use, could take all the water in a watercourse to the detriment of downstream users. In response, California adopted a constitutional doctrine that water use must be reasonable as well as beneficial.

Compounding the complexity of water rights in California, there has been an over-allocation of water rights. In some cases, persons along a watercourse collectively had “rights” to several times the amount of water that actually existed. Decisions were made on belief that sufficient amounts of water would be available.

During times of shortage, the priority system was supposed to control the allocation of water. In actuality, this system has proved to be inadequate to the task. Cutting junior water right holders entirely, while allowing seniors to divert without restriction, led to inefficient and inequitable decisions.

Water wars invoking competing water-right principles have broken out during the drought. For example, water-right holders can divert natural flows in a watercourse. But they are not supposed to divert water that has been released from storage in reservoirs located upstream. In reality, water courses are commingled with both natural flows and storage releases. Figuring out who has the right to use such water is problematic, to say the least.

Adding further to the complexity is the fact that much of the water used in California comes from underground. Groundwater use in California, at least until recently, has largely been unregulated. Whoever can drill the deepest water well can often take all the water needed. This has led to serious over-drafting of groundwater: More water is being taken out of the ground than is being replaced naturally.

Given all the complexities and uncertainties, making sound, equitable, efficient water-allocation decisions based on the existing water-right priority system is unlikely. Rather, decisions are often being made on a case-by-case basis, each being contested by competing water interests.

If the present water-rights priority system does not work in times of shortage, is there a better way? The answer may involve expanded use of the state’s “reasonable water use” doctrine.

The reasonable-use doctrine is embedded in the state’s constitution. It has been routinely upheld by the state’s highest courts. In fact, court decisions have broadly interpreted the breadth of the doctrine, and have provided a road map as to how it could be used during the drought to facilitate better water-use allocation decisions. It is California’s super water right.

Under this doctrine, all water use in California, no matter how senior the right, must be “reasonable.” Government has been given sweeping authority to invoke the right. Importantly, the reasonable-use doctrine can be adjusted to fit the circumstances. That is, what might be considered a reasonable way to use water in normal situations could be considered unreasonable during drought.

The doctrine has been used a couple of times during the current drought to modify the priority system. In one case, use of water for frost protection on crops was curtailed based on the unreasonableness of that use: It left various watercourses without enough water to support other beneficial uses, including fish health.

Given the severity of the drought, the doctrine can and should be used more expansively. Instead of using the water-rights priority system to make decisions on whose water use should be curtailed, the reasonable use doctrine can be invoked to make more equitable decisions.

Senior water holders and groundwater over-drafters can have their water use restricted during times of drought. The inefficient use of water should be considered unreasonable.

For example, flood irrigating a field during drought can be considered unreasonable. Likewise, so could taking twice as much water out of a groundwater aquifer as is naturally replenished with no plans to make up the difference.

Employing the reasonable-use doctrine in a more comprehensive, forward-looking way will require a new mindset by the State Water Resources Control Board. The fact that the State Water Board has successfully used the doctrine in a few modest ways during the drought may embolden its use on a broader scale.

In these and other ways, the reasonable-use doctrine can become what it should be: a vehicle for making better water-use decisions during these times of water shortage.

Craig Wilson was chief counsel to California’s State Water Resources Control Board and recently retired as the state’s first Delta watermaster, a position established by 2009 legislation to manage water rights in the Sacramento-San Joaquin Delta.

Photo courtesy of Craig Wilson