Understanding Groundwater Law

Groundwater does not usually conform to property lines. It flows through layers of soil, rock, springs and caves and obeys hydrological and geological principles, not human laws or boundary lines. Establishing and understanding laws around groundwater ownership and management can become very confusing very quickly. 

As increased water demand and pressure on surface water supplies raise the value of groundwater resources, understanding groundwater laws and precedents matters even more. 

In Texas, groundwater law has largely been decided by the judicial system, and the Texas Legislature has passed few groundwater-related bills. The resulting myriad of precedents presents challenges to groundwater users.

“They came to be through a mix of case law and legislation that have evolved over time, which makes it even harder to wrap your head around," said Amy Hardberger, J.D., a professor of water law and director of the Center for Water Law and Policy at Texas Tech University. “Then the presence of groundwater conservation districts adds another layer of regional variability. So, when somebody says, well, what is the groundwater law of Texas? It's like, how much time do you have?”

The current systems

Federal guidelines leave groundwater law and management up to each state. While the U.S. government can sometimes weigh in on issues involving multiple states, international boundaries or endangered species, groundwater law is largely at each state’s discretion. 

“It's important to know that all water law is basically a state issue and highly regionalized,” Hardberger said. 

Estimated reading time: 8 minutes

Legal statutes and precedents governing groundwater vary among states and can be challenging for residents to navigate

More Information

• US Groundwater Laws, TAMU
• A Primer on Groundwater Law
• Who Owns the Water?, Texas: The state of water
• Greener Guidance: Groundwater Regulations, National Association of County and City Health Officials (NACCHO)

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There are four general approaches to groundwater ownership that states follow. While some states use a combination of approaches, these are the most helpful to learn when it comes to understanding groundwater law.

  

  

Rule of capture

Absolute dominion, or rule of capture, is how Texas has decided groundwater ownership for more than a century. (See the East decision in "Texas' Most Infamous Groundwater Lawsuits.")

"The Texas approach is: if you own the land, then you own the groundwater that's underneath your feet.”

“The Texas approach is: if you own the land, then you own the groundwater that's underneath your feet,” said Gabriel Eckstein, J.D., a professor in the Texas A&M University School of Law and director of the Energy, Environmental and Natural Resource Systems Law Program. 

  

  

Reasonable use

Reasonable use, sometimes called the American rule, is similar to absolute dominion, with a few limitations. In this approach, either the state owns the groundwater, or the groundwater is “unowned” until captured, Eckstein said, but landowners have the sole right to access the groundwater below their land. This approach is the most common in the United States, used by 17 states. 

Hardberger said this doctrine provides clarity in disputes between water users. 

“We now have a little bit of a relationship that we pay attention to between these two users,” Hardberger said. “So, you can't use an unreasonable amount or amount that unreasonably interferes with somebody else's use of their water.”

  

Prior appropriation

Prior appropriation is used mostly in western states, and it involves more management of groundwater sources than the previous two laws. 

“It’s basically first in time, first in right,” Eckstein said. “Meaning, if you have a list of who got their water first, the first person on the list is going to get 100% of their water right.

“So long as there is enough water in the river (or aquifer), every prior appropriation holder will get 100% of the right they claimed through the process,” he said. “However, when you have a shortage, e.g., due to over-allocation or during a drought, all of the rights holders who have the earliest rights get 100% of their right. Eventually, as you work your way down the list based on the priority date, you run out of water. When you run out of water, everyone from that point on the list and everyone with a younger right gets 0% of their right.”

  

Correlative rights

Correlative rights is the fourth type of groundwater law and is a mix of the previous three.

Under a correlative rights framework, users who obtain groundwater rights for use on land overlying that aquifer will share proportionately when water supplies are scarce. But, they always have priority over those who use the water on land that does not overly the aquifer. Off-site groundwater use, in which groundwater is pumped and then transported to land not above that aquifer, is treated under the prior appropriation system by the managing authority. 

“Water that is used off-site, on land not overlying the aquifer, that's the right that is going to get cut first because it's the lowest on the priority list,” Eckstein said. “So, this approach combines two or three of these rules.”

  

 

States tend to follow one of these four types of groundwater law, but as groundwater science has evolved and water demand has increased, states are more frequently using hybrid approaches. 

How state groundwater laws evolve 

Each state handles its own groundwater law and management systems. But how do those decisions come to be?

“Most of the states started with absolute dominion because it's part of English common law, which they adopted when they joined the United States,” Eckstein explained. “Common law is what some people tend to call judge-made law. It happens when the courts develop their own legal system in the absence of legislated rules. And since the rule of capture for groundwater was part of the law in England, we borrowed it and applied it here.”

Since then, most states have moved away from the rule of capture. Only a small handful have kept it
in place. 

“Some of them still use it. They think `Why should we change?’” Eckstein said. “Some states have so much surface water, that groundwater is not a big issue for them.”

States with higher groundwater demand have adjusted laws to address disputes and interference between neighbors. 

“When you move further south and west, a lot of the states have changed to the reasonable use rule because they started to get disputes. They wanted to come up with a way to still respect ownership, because this is the United States and property is important, but give some kind of reasonableness test to the use,” Eckstein said.

Economics also affect states’ groundwater approaches, he said.

“Moving further west, you have less and less water, and some states, again, mostly in the west, wanted to promote economics, but also wanted to apply a reasonableness or beneficial test to the use,” Eckstein said. “And that's how they came up with prior appropriation.” 

Correlative rights is another way of looking at the same water problems that prior appropriation addresses.

“These states had the same justification, not a lot of water and the desire to develop,” Eckstein said. “They also wanted to be able to use water off-site. As a result, it created all sorts of complicated variations.”

While groundwater managers face droughts, weather variability, population increases and higher water demand, these realities have mostly not yet affected groundwater law, Eckstein said, because enacting any major changes is difficult and slow.

“Trying to tweak these laws now is really hard,” he said. “And this is where some states are.”

  

Crossing state lines

Groundwater does not follow state lines, and many states face interstate aquifer challenges.

“We have dozens of interstate compacts on surface water — Texas has a compact with Oklahoma on the Red River, with New Mexico on the Pecos River, and with New Mexico and Colorado on the Rio Grande,” Eckstein said. “But there's never been a compact for groundwater in the United States.” 

This is in part because there have never been legal disputes between states when it comes to groundwater until recently.

In 2014, the state of Mississippi sued the state of Tennessee for allegedly pulling more groundwater from Mississippi than they should have.

This case found its way to the U.S. Supreme Court, where in 2021 it was ruled that the law applied to interstate groundwater should be the same as to interstate surface water.

“That rule is called equitable apportionment. We apportion the water equitably, in a fair manner. How you determine what is fair is mostly based on economics — who's making the best use of the water, producing the most economic benefits, or has the highest economic value.”

“That rule is called equitable apportionment. We apportion the water equitably, in a fair manner. How you determine what is fair is mostly based on economics — who's making the best use of the water, producing the most economic benefits, or has the highest economic value,” Eckstein said. “This is the first time it's ever been applied to groundwater. It's the first time a case like this has ever gone to the Supreme Court.”

Why understanding groundwater law matters

Court cases continue to shape states’ groundwater law and management.

One such recent case is Texas v. New Mexico and Colorado, ruled on by the U.S. Supreme Court in June. The Court rejected the states’ proposed settlement for shared water in the Rio Grande Basin and set precedent for the federal government’s potential involvement in future multistate groundwater disputes.

Ordinary Texans seeking to steward their groundwater resources while also sustaining profitable working lands may find it challenging to understand Texas’ groundwater laws.

“I think this is one of the biggest challenges we have in Texas, because our groundwater rules are complicated,” Hardberger said. 

"If every Texan even understood that very, very basic thing, we would be better off. Unfortunately, a lot of times, people don't realize how we regulate groundwater until it hurts them.”

Hardberger explained that at its core, groundwater law can be boiled down to one thing for Texans.

“It's just property rights,” she said. “It defines who gets access to water, how much, what can they do with it? What are the limits of that? That is the guiding principle.”

Knowing even the general rules of Texas water law can help Texans avoid difficult situations.

“Texans need to understand the rule of capture and that, generally, allows a tremendous amount of pumping legally, which can cause problems,” Hardberger said. “And then, understand that there might be regional regulation that may change that. If every Texan even understood that very, very basic thing, we would be better off. Unfortunately, a lot of times, people don't realize how we regulate groundwater until it hurts them.”