The landmark event began Sunday afternoon and by 9am Monday, there was 186 mms of water topping the dam wall, according to Orange City Council.

Mayor Reg Kidd and Council CEO David Waddell held a mid-morning media event at the dam to mark the event.

"A hell of a lot is going over. I'd say what Orange would use in one day is going over there in a couple of hours," Cr Kidd said.

"Only about two years ago we were facing fairly severe restrictions but since those days we've got storm-water harvesting and pipelines.... which supplement our water [storage]."

The last time water flowed over the dam wall was in July 2016.

Cr Kidd added that the dam had reached the 80 percent mark around three and a half weeks ago before getting to 90 percent on July 11.

"There were predictions that it could take much longer to top the wall, but the ground is so wet anywhere around Orange that we're reaping the benefit of any run-off," he said.

Despite reaching the water storage milestone, minor water restrictions will remain in place with the Permanent Water Savings Standards which operate under the same criteria as Level Two Water Restrictions.

"These standards are about the change in mind-set and attitudes about water. Even when our dams are full we want to be sensible with our water use," Cr Kidd said.

"Orange residents lead the way when it comes to low water use and we want to keep doing that despite flowing over the dam wall."

Permanent Water Savings Standards will be in place until the water storage level drops to 70 percent, at which point the city will enter Level Two Restrictions.

The only difference between the two standards is that there is no time restriction on car washing under permanent water saving standards.

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