How water rights work in the western US
In most of the West, owning land does not by itself give you the water that crosses it or lies under it. Water belongs to the public, and the state grants the right to use a defined amount of it for a defined purpose. That right has a date, a source, a place it is taken from and a place it is used, and it can be bought, sold, changed or lost separately from the land.
Prior appropriation
Every state on this map uses the prior appropriation doctrine for surface water: the first person to put water to beneficial use holds the senior right, and later users fit in behind them. In a short year the shortage is not shared evenly; junior users are cut off so seniors get their full amount. The doctrine grew out of mining camps and irrigation in the 1800s, which is why so many senior rights on the map date from then.
California is the main exception in the region: it recognises riparian rights, which come with land that borders a stream, alongside appropriative rights. Groundwater varies even more. Nebraska manages it through local natural resources districts rather than by priority, and Texas follows a rule of capture overseen by groundwater conservation districts.
Where the dates come from
Older rights often began as use, not paperwork, and states have spent decades turning that use into a court record through adjudications. Montana, Idaho and Oregon have run or are running basin-wide adjudications; Colorado decrees rights in its water courts. Newer rights start as an application to the state, become a permit, and are confirmed by a certificate or license once the water is shown to be in use. Each state's guide explains which of these record types appear in its data.
Use it or lose it
A right is measured by beneficial use. Rights that sit unused for long enough can be found abandoned or forfeited, on rules and timelines that differ by state. A record on this map being active means the state has not ended it, not that water is being used.
The terms on each record
What does a dot on the map mean?
Each dot is a point of diversion: where the state's record says water is taken from a stream, spring, reservoir or well. It is not necessarily where the water is used, and a dot inside a property line doesn't mean the right belongs to that property. One right can have several points, and one point can serve several rights.
What is a priority date?
The date that sets a right's place in line. Depending on the state and the kind of right, it is when the water was first put to use, when a claim says use began, or when an application was filed. Older dates are senior; newer ones are junior. The colours on the map run from dark blue (oldest) to orange (newest).
First in time, first in right
This is the prior appropriation doctrine that governs surface water across most of the West. When a stream can't supply everyone, the most senior right gets its full amount before the next one gets any. In a dry year a senior user can “make a call”, and the state then orders junior users on that source to stop diverting. Seniority only matters among rights that draw on the same water, which is why each record links to the other rights on its source.
cfs, gpm and acre-feet
cfs (cubic feet per second) is a rate of flow: 1 cfs is about 449 gallons per minute (gpm), and running for a full day it moves almost 2 acre-feet. An acre-foot (AF) is a volume, enough to cover one acre a foot deep, about 325,851 gallons. A right usually caps both: how fast you may divert and how much in a year.
Surface water and groundwater
Streams, springs and reservoirs are surface water; wells draw groundwater. Most states on this map run both through the same priority system, but not all: Nebraska's groundwater is registered with the state and managed by local natural resources districts, without priority dates. Where groundwater feeds a stream, states may treat a well as part of that stream's line.
Exempt and domestic wells
Many states let a household drill a small well without a full water-right permit, inside limits that differ by state, and some of those wells still have to be registered or noticed. Utah has no such exemption at all. The limits for each state are on its guide page. A small well that was never filed won't appear on this map.
Priority date · senior to junior
- Before 1880
- 1880–1899
- 1900–1919
- 1920–1949
- 1950–1972
- 1973–1999
- 2000 and later
- No priority date