A five-year fight over excess water in WA has been settled.

Irrigators in WA's far north have had their dispute over water allocation upheld in the State Administrative Tribunal.

The court was asked to rule on a stoush between the Ord Irrigation Co-operative (OIC) and the Department of Water and Environmental Regulation over which has the right to excess water.

The OIC runs water delivery for more than 100 properties in the first stage of the Ord River Irrigation Area, and to Ord Stage Two developer, Kimberley Agricultural Investment.

The dispute erupted in 2015, when the OIC's annual water licence of 335-gigalitre was cut by 30 per cent by the department.

The department felt that irrigators were not using the full water allocation, and that the unused water should be controlled by the department.

The OIC disagreed, taking the decision to the SAT, the Court of Appeal, and then back to the SAT last year.

The tribunal this week determined that the correct and preferable decision was that the water licence should be renewed for 10 years at the original 335gL rate.

The tribunal noted in its judgement that there were no competing users or uses for the unused water.

OIC chairman David Menzel said it was a relief.

“Absolute sense of relief is the overwhelming emotion at the moment,” he said.

“You start to doubt yourself and you wonder if, with all the people involved, whether you're actually on the right track.

“The judge's decision reflects a lot, if not all, of what we were arguing.”

He said the OIC could now grow.

“Five years is a long time to be tangled up in legal proceedings,” he said.

“We've paid well over a 100 per cent of a year's income on legal expenses over the past five years — that's a huge knock to our business.”

The OIC's arguments focused on the need for water security for farmers and investors.

OIC lawyer Faye Ashworth said farming in the Ord is expensive due to its remote location, so flexibility with water is needed to help farmers grow to economies of scale and potentially change crops depending on market prices.