The tricky question of water rights on Mars.

If There Is Water on Mars, Who Gets to Use It?

If There Is Water on Mars, Who Gets to Use It?

The citizen’s guide to the future.
Nov. 2 2015 7:33 AM

If There Is Water on Mars, Who Gets to Use It?

The future of human colonies on the Red Planet depends on the answer to that question.

Water on Mars.
In this handout provided by NASA’s Mars Reconnaissance Orbiter, dark, narrow streaks on the slopes of Garni Crater are inferred to be formed by seasonal flow of water on surface of present-day Mars.

Photo by NASA/JPL-Caltech/University of Arizona via Getty

Humans settle around water, especially in the desert. Indeed, our earliest civilizations developed around desert water bodies like the Nile, Tigris, and Euphrates. With NASA’s recent discovery of evidence of liquid water on the desert planet Mars, a new extraterrestrial civilization could arise on Mars, and it will almost certainly be near a Martian lake, river, or well. Let’s assume for the sake of argument that the water is potable, or at least can be treated and become usable for human purposes. In that case, who has the right to this water, and how should it be allocated? Perhaps the answer lies in a 19th-century U.S. water law policy designed to encourage the innovations and entrepreneurialism necessary to explore and colonize the American West.

In the 19th century, the United States acquired enormous tracts of undeveloped desert land. Under the banner of Manifest Destiny, American leaders created policies to promote settlements in the arid region. Key among those policies was an innovative approach to water rights—the law of prior appropriation, under which the first person to capture a quantity of water and put it to beneficial use had superior rights to that quantity of water than all other subsequent users. This regime provided an incentive for smart, industrious people to run as fast as they can into the desert, an attitude that was essential to achieving the aims of Manifest Destiny. A water user’s right dated back to the day the user first attempted to divert water for beneficial use, so long as the user was diligent from that day until finally putting the water to beneficial use. For example, if a settler in Arizona began digging a diversion ditch on the Gila River in June 1875 and worked on that diversion until finally irrigating crops in December 1875, he would have a superior water right to another person who diverted in July 1875 and began irrigation in November. Prior appropriation was an orderly way to encourage industry to subdue a harsh desert.


This might be just the answer to the question of how we create incentives for people to undertake the incredible expense and risks required to settle the red planet. If the international community knew that the first nation (or company) to capture a quantity of Martian water and put it to beneficial use had superior rights to all subsequent users, it could spur the types of innovation and entrepreneurialism needed for interplanetary exploration and colonization. Human curiosity and the impulse to explore will likely motivate some efforts to reach Mars. But those could range from the credible but politically complicated NASA missions, to less realistic endeavors, like those of Mars One. But a sustainable investment in the development of Mars will likely require stronger incentives. Under a prior appropriation water rights regime, those who invest in the first successful venture to Mars and actually use Martian water would have superior rights to any subsequent users. The first mission to Mars would have to include drilling a well or installing a pump or diversion ditch on a stream. But those first water users would have to remain diligent in developing the resource until it was put to beneficial use, or risk losing their water priority. This would encourage long-term planning for multiple missions to Mars.

Of course, a Martian prior appropriations water rights regime would require a change in international law, which currently forbids any nation from claiming extraterrestrial resources. While this law has value—in avoiding over-exploitation or inequitable exclusivity in extraterrestrial resource rights—it does little to encourage investment in developing those resources. Prior appropriation would create incentives to invest in the exploration of Mars.

Thinking about water rights on Mars is valuable for three reasons. First, missions to develop Martian natural resources may be lucrative business in the future. Mars has potentially valuable mineral resources, including copper, zinc, gold, and the kinds of rare earth minerals used in lasers, microelectronics, and batteries. Indeed, these rare earth minerals are so rare, we may end needing to leave Earth to find a long-term supply. Second, someday interplanetary colonization may be essential for the survival of the mankind. Third, and of more immediate concern, contemplating the water rights regime on Mars may help us better understand what we did right, and what we did wrong, in establishing the prior appropriation regime in the western United States and how to think about the changes to water law that may be necessary to adjust to a changing climate.

While a prior appropriation system creates strong incentives for a new Space Race, it has potential problems. We need look no further than the ongoing drought in California for evidence of the ways prior appropriation can fail to serve the public interest. A farmer with water rights dating back to 1875 may use inefficient irrigation methods and grow low value crops. But that farmer may still insist on his rights, leaving junior right holders—even if they want to use the water for homes, schools, and hospitals—high and dry. Prior appropriation on Mars could lead to the first Martian mission using water for mining operations, and then that operation could assert superior rights to future missions of scientific exploration or colonization. Furthermore, prior appropriation law typically includes the concept of forfeiture, which means that if a water right holder fails to use its right for a period (say five years), it loses its water right, and that water becomes available for other lower priority users to claim. As a result, water rights holders have little incentive to be efficient in their water use; if they don’t use it, they lose it.


Perhaps the biggest challenge to a prior appropriation regime on Mars is that there is no existing government there to say what uses are “beneficial” and how to prioritize among competing uses. Even in the highly competitive world of water rights in the western U.S., each state holds water resources in trust for the benefit of its citizens, and prior appropriation rights are only the right to use a state-sanctioned amount of water for a state-approved beneficial use. States, along with the federal government, regulate water quality as well, both to protect human water uses and ecosystems that depend on the water. But on Mars, there is no state to act as that trustee to preserve water quality and prioritize water uses and no humans or ecosystems to protect.

A few measures would help the world create the incentives of the prior appropriation regime, while avoiding the mistakes in implementation that plague western water law today. First, the United Nations could be designated as the trustee of extraterrestrial water for purposes of determining beneficial use, with the International Court of Justice adjudicating disputes over those water rights. Water rights owned, but not used, by states or companies could be held temporarily in trust by the U.N. for research purposes and shielded from forfeiture. Then, if colonization creates a demand for domestic water, and water rights holders will not sell or lease the water, the U.N. could condemn a limited percentage of water rights by paying right holders the fair market value of those rights, or else those companies can lease or sell water rights to colonizers. Finally, the U.N. could issue permits for water use that impose best management practices to encourage sustainable management and avoid contamination.

For example, imagine a large mining company invested in a mission to Mars. It secured first-priority rights to use a large quantity of Martian water to mine for neodymium, a rare earth mineral used in lasers. The U.N. would permit the use of that water, with the requiring that certain best management practices to promote efficiency and avoid contamination. Later, mass colonization on Mars shifts priorities to domestic water uses. The U.N. could then condemn a portion of the mining companies’ water rights by paying the company the value of those rights.

These measures could spur an international interplanetary Manifest Destiny, while still protecting Mars from invading Earthlings—and the invading Earthlings from themselves.

This article is part of Future Tense, a collaboration among Arizona State University, New America, and Slate. Future Tense explores the ways emerging technologies affect society, policy, and culture. To read more, visit the Future Tense blog and the Future Tense home page. You can also follow us on Twitter.

Rhett Larson is a professor at Arizona State University Sandra Day O’Connor College of Law.