Five water main breaks on Oahu last week snarled traffic and disrupted service, but officials say the final tally for main breaks in 2012 is still expected to come in way below totals seen in previous years.

As of Oct. 31 there were 263 water main breaks on Oahu this year, according to the Hono­lulu Board of Water Supply. Last year the number hit 300.

That’s way down from a 10-year high of 500 in 2002 and an annual average for the decade of 368.

Ernest Lau, BWS manager and chief engineer, attributes the decline in main breaks to infrastructure improvements and lower water use.

"What we’re seeing is probably a combination of things," he said.

Still, further decreasing the number of main breaks each year is a major goal of a five-year, $345 million capital improvement plan that BWS kicked off in mid-2011. The CIP plan includes replacing 40 miles of pipeline and repairing 216 wells and booster stations.

The efforts are aimed at building on the CIP gains made from 2005 to 2010. Over that period, crews repaired 35 miles of pipeline and fixed or replaced 64 wells and booster stations.

Lau said there are a host of causes for water main breaks — from the age of the line to how much water is being pumped.

And while the CIP plan and other projects, including a leak detection program, will probably help prevent a number of main breaks, "we can never achieve zero main breaks a year," he said.

"At this point I’m not sure where my comfort level is as far as the number of breaks per year," he added.

Preventing breaks, Lau said, requires a multipronged approach that includes infrastructure improvements, water conservation and engineering solutions.

And those efforts have to be balanced with how much customers are willing — and able —to pay for water.

"At the end of the day, we need to balance the quality of service, the number of breaks, with the affordability of our customers," he said.

Last year the Board of Water Supply approved a 70 percent increase in water rates over five years, in part to help pay for capital improvements. The board is also eyeing the possibility of redeveloping parking areas at its Beretania Street complex as a way of generating revenue.

Water main breaks are a perennial problem in part because of aging infrastructure. The board oversees about 2,100 miles of pipeline islandwide, and about half of those pipes are more than 40 years old.

In recent years BWS has had about 14 to 18 water main breaks per 100 miles of pipeline.

The national average for water utilities is 25 to 30, according to the American Water Works Association, an industry organization. But the group is quick to point out that not all utilities characterize breaks in the same way.

In addition to increased infrastructure work, the BWS attributes the decline in water main breaks to a drop in water use.

Last year 135 million gallons per day were pumped through BWS pipes, from 144 million gallons the previous year and 154 million gallons in 2007.

"With a stabilized water demand, that means we don’t have to pump as much," Lau said.

The reason for the drop is unclear but could relate to better conservation or a desire by consumers to save money, officials said.

The five breaks that happened last week were scattered around the island, and causes for the breaks were not immediately available.

On Monday a 64-year-old, 8-inch water main on Ahua Street in Mapunapuna broke, closing the road and affecting area businesses.

A day later there was a 16-inch water main break near the Wai­anae Fire Station, cutting service to about 400 customers. One lane of Farrington High was closed for hours, and classes at Wai­anae Intermediate School were canceled.

Also on Tuesday, two 8-inch water mains broke — one in Makiki and another in Nuuanu.

Finally, on Wednesday a 6-inch water main broke on Kamehameha Highway in Kaneohe but did not cut service to any customers.