Last verified Jul. 2026

Prior appropriation: first in time, first in right

The rule, in the constitution that created it

Colorado wrote this into its founding document in 1876. Two sentences do most of the work — one making the water public, the other making priority the way it is divided:

That is the whole doctrine in a line: priority of appropriation shall give the better right. The legislature restated it in the 1969 act that still governs administration today, adding that tributary groundwater is part of the same system.

Why Colorado did it this way

The eastern states inherited riparian rights from English common law: if a stream touches your land, you may make reasonable use of it, and everyone along the bank shares the shortage. That system assumes rain. Colorado's founders did not have rain. Mines and farms sat miles from any stream, and the water had to be carried to them in ditches — which is worthless if the person who dug the ditch can be cut off by someone who buys streamside land later.

The Colorado Supreme Court settled the question in Coffin v. Left Hand Ditch Co., decided December 15, 1882, holding that the riparian doctrine had never applied in Colorado and that the first appropriator of water for a beneficial purpose holds the prior right. Coffin v. Left Hand Ditch Co., 6 Colo. 443 (1882) The reasoning was frankly geographic: in a place this dry, artificial irrigation is a necessity rather than a convenience, and a rule that ties water to riverbanks would leave most of the state's productive land useless.

What "first in right" means when the river runs short

This is where prior appropriation stops being an abstraction. When there is not enough water, Colorado does not divide the shortage evenly. The most senior right takes its full decreed amount; the next takes its full amount; and so on down the list until the water runs out. Everyone below that point gets nothing.

The mechanism is a call. A senior right that is not getting its water calls for it, and the division engineer orders junior diversions upstream to shut down until the senior is satisfied. That authority is statutory, and it is not discretionary:

How a date becomes a number

Seniority is administered in the field by an administration number, which is just the appropriation date expressed as a count of days since December 31, 1849. Smaller means older means better.

You can watch the arithmetic work on a real record. The Boulder and Larimer County Irrigating and Manufacturing Ditch, on the Little Thompson River, holds a right appropriated 1875-06-30 and carries administration number 9312.0 — exactly 9,312 days after December 31, 1849. A second right on the same ditch, appropriated 1877-05-20, carries 10002.0, and 10,002 days is exactly that date. DWR HydroBase · WDID 0400588 · verified Jul. 2026

There is a wrinkle worth knowing, because it explains why some very old rights sit surprisingly low in the pecking order. A right that was appropriated early but adjudicated in a later proceeding is administered behind rights confirmed in earlier proceedings — the postponement doctrine:

In DWR records those rights show a compound administration number with a decimal component. The lesson for a buyer is simple: read the administration number, not just the appropriation date on the listing. Reading a decree covers where to find both.

The two things people get wrong

"Domestic use beats everything"

Article XVI § 6 does contain a preference: when a stream cannot serve everyone, domestic use is preferred over other uses, and agricultural use over manufacturing. But this is a narrow preference between competing appropriators, not a general license for a city to take a farmer's water. In practice a municipality that wants an irrigator's senior right buys it and runs a change case through water court — it does not simply invoke the preference.

"It's my land, so it's my water"

Never true in Colorado. The stream through your property belongs to the public; the well under it draws water that is presumed tributary to that stream; and the rain on your roof is part of the same system, which is why rain barrels needed their own statute in 2016. What you can own is a right to use a measured quantity, in priority, for a decreed purpose. The rest of the basics works through what that ownership actually consists of.