Almost 1,100 students at Queen Creek Middle School had an unexpected day off Thursday after a nearby water main broke early that morning.

The school's closure postponed a day of Arizona's Instrument to Measure Standards, or AIMS, testing. The testing will resume today and be made up on Monday, Principal Denise Johnson said.

School officials made the decision to close the school after they were told water would not be turned on until about noon. The water was turned back on about 11 a.m., Johnson said.

Without water, Johnson said, the school had a safety and sanitation problem as the fire sprinkler system and faucets and toilets would not be able to work.

Some students already on buses were taken back home, while others waiting for the bus were told by bus drivers that school was canceled. The majority of the families were reached by school staff to tell them of the closure, Johnson said.

A letter will also be sent home with students today.

The main break also caused the water to be turned off until about 3 p.m. at the Queen Creek Unified School District office and a farming business at Ellsworth and Rittenhouse roads.

This is the first time the district had to close a school during the crucial weeklong AIMS testing period, said Tom Lindsey, the district's director of curriculum and instruction.

"It always seems to be interesting challenges that occur during this time," Lindsey said. "We certainly couldn't have students on campus. School safety is most important."

The water main break was on the southwest corner of Queen Creek and Ellsworth roads across the street from Queen Creek Middle School. It was caused during construction on a separate waterline that is part of a joint project between Gilbert and Chandler for a new water treatment plant. The waterline is being installed from Pinal County about a mile east of Schnepf Road to the $100 million plant at Higley and Ocotillo roads, which is scheduled to open in mid- to late 2009, said Gilbert spokesman Greg Svelund.

Paul Gardner, Queen Creek's water director, said the problem was exacerbated further because the town heard about it after the fact, and road widening and paving in the area covered up several water valves.

"We would have had that turned off in 10 minutes, but we had to go to the next series of water valves," Gardner said. "We had to shut off the water so we didn't have to shut the road down."

About 800,000 gallons of water flooded the area, he said.

"Sometimes these things just happen," Gardner said. "We do our best to try and mobilize things."