During the lead-up to and analysis of the 2016 U.S. Presidential election, the United States was subdivided along almost every possible demographic category in an attempt to predict and understand the election outcome. Were water managers to construct electoral maps, they would use water rights to show instead that the county is divided geographically just west of Minnesota, Iowa, Missouri, Arkansas, and Louisiana (Fig. 1).

Fig. 1  Water rights in the United States shown as electoral votes.  Based on [1].  [Note]
Water rights in the U.S. generally fall under two doctrines, termed “Riparian Rights” (blue states with 352 electoral votes) and “Prior Appropriation” (red states with 119 electoral votes).   A few states us a hybrid of the two (yellow states). If you’ve only ever lived on one side of the divide, you might be completely unaware of how the other half lives.  Both these doctrines strongly influence how the public and government view and manage water as a natural resource, especially during droughts.

Riparian Water Rights

Riparian rights states make up roughly the eastern half of the U.S.  Riparian rights were the first set of principles that governed water use in the U.S. and derive from English common law.  Because of this, it is not surprising that riparian rights states tend to include the original British colonies and other places with early statehood.

Under Riparian water rights, landowners whose property borders a body of water, i.e. in the riparian zone, have a right to make reasonable use of its water as long as this use doesn’t interfere with the rights of those downstream.  This provides courts significant flexibility to determine what constitutes a “reasonable use”.  In its strictest form, water during a drought is apportioned based on the frontage of each property to the water body.  More recently, most riparian states have set up permitting systems to better decide what a reasonable use is, how a water withdrawal benefits society, and how it would affect other users in the system.  This system, termed “regulated riparian” [2,3], has proven effective for this region, partially because water issues tend to be less severe in the temperate eastern U.S., which typically receives 3-4 times the mean annual precipitation of the more arid west (Fig. 2).

Fig. 2  30 year mean annual precipitation [PRISM].

Prior Appropriation

Water rights in western U.S. states instead follow the principle of Prior Appropriation.  This doctrine follows the principle of “first in time, first in right” and can be traced back to the early gold mining camps of California and Colorado. In more formal terms, prior appropriation states that if a person diverts water and puts it to a beneficial use, such as irrigation or municipal/industrial use, they acquire a continuing right to that amount of water. That right supercedes the rights of later users during a shortage.  In the more arid west where water was needed to irrigate land not adjacent to rivers, this principle provided a better guarantee of water and encouraged the migration of Americans to the west.

Prior appropriation is a priority system, based on the date of the original claim, known as the “priority date”. Some claims extend back to the 1850s [4]. As a simple example of how prior appropriation works, imagine that Users A, B, and C have water rights of 30 cfs, 20 cfs, and 10 cfs, respectively extending back to 1870, 1940, and 1980.  During a year when flow is 70 cfs, all users would receive their water, but during a drought when flow is only 40 cfs, User A would receive the full 30 cfs, User B would receive the remainder of flow (10 cfs), and User C would receive no water. Rights remain with the property indefinitely if they are put to beneficial use, though there are some mechanisms for transferring rights or declaring a right abandoned, typically after 5-7 years without use [5].

The frequency of junior parties having their water rights curtailed has been somewhat reduced by construction and better water management of large carry-over storage reservoirs.  Also, the strict interpretation of “beneficial use” has been reinterpreted by some western states since the 1990s to include enhancing wildlife habitat and recreation [6,7].

Hybrid Systems

There are also several states that have adopted a hybrid water rights system.  The most notable is California, where reasonable use riparian rights receive first priority and appropriative rights receive second priority during disputes.  Nebraska also has a dual system, which came about after the state shifted from a riparian system to prior appropriation, but retained the legal rights of both [8].  There was a transition from riparian system to prior appropriation in other states (e.g. Kansas, Texas, North and South Dakota, Oregon, Washington), but these states generally converted entirely to prior appropriation, with the riparian users grandfathered into the new system.  It is also important to note that groundwater law does not necessarily follow the state-by-state division between riparian and prior appropriation doctrines, leading to other interesting mixtures.

Coming together

The systems of riparian rights and prior appropriation are deeply entrenched in state laws and it is unlikely that these policies will change.  So, drought and water issues must be addressed differently in the two regions, working within their respective frameworks.

As both regions seek to deal with increasingly complex water challenges [9,10], the two policies have borrowed ideas from each other.  For instance, riparian states are increasingly relying on permit systems that define and prioritize beneficial uses, while prior appropriation states are loosening their definitions of beneficial use to recognize in-stream uses as deserving of protection.  In this way, the red and blue states on our map have structurally different approaches to manage water, but increasingly make use of what other states have to offer.


  1. This is a simplification in order to classify states into general groups.  Each state has unique water laws and I recommend you research your own state. Iowa is sometimes considered a hybrid water law state, but its surface water laws are closer to regulated riparian, which is why it receives this designation here.

Recommended Links


  1. Christian-Smith, J.  and Gleick, P.H. (2012)  A Twenty-First Century US Water Policy. New York: Oxford University Press.
  2. Beck, R. (2000) The Regulated Riparian Model Water Code: Blueprint for Twenty First Century Water Management. William and Mary Environmental Law and Policy Review 25(1).
  3. Dellapenna, J.W. (1994) The Regulated Riparian Version of the ASCE Model Water Code: The Third Way to Allocate Water.  JAWRA. 30: 197-204.
  4. Colorado Foundation for Water Education (2015) Citizen’s Guide to Colorado Water Law, Fourth Edition. ISBN 978-0-9857071-2-5
  5. Szeptycki, L.F., Forgie, J., Hook, E., Lorick, K. and Womble, P. (2015) Environmental Water Rights Transfers: A Review of State Laws. Water in the West.
  6. Deason, J.P., Schad, T.M., Sherk, G.W. (2001) Water policy in the United States: a perspective. Water Policy. 3: 175-192.
  7. Neuman, J.C. (2000) Protecting Instream Flows in Prior Appropriation States: Legal and Policy Issues. Water and Growth in the West.
  8. Rozmarin, G. (1968) The Dual-Sysstem of Water Rights in Nebraska. Nebraska Law Review 48(2).
  9. NPR (2013) Water Wars: Who Controls the Flow?
  10. Lustgarten, A. (2015) Use It or Lose It. Propublica.

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