FARMINGTON — Cold weather has not affected the city's water mains, but officials say that about 80 miles of aging cast-iron pipes are still vulnerable.

In the short term, the city's Public Works Department is continuing to monitor its water and wastewater system. Officials also urge residents to set their faucets to drip overnight to avoid residential water pipe breaks.

"We're anticipating more private freezing," said Ruben Salcido, the city's water and wastewater operations manager and environmental coordinator. "(Dripping) minimizes the chance for breaks."

The city's water and wastewater utilities usually experience more problems during periods of greater temperature fluctuation, he said.

"It's the temperature changes that affect the cast-iron pipes," Salcido said. "During the late fall and early spring, we get the most breaks. You're going to get water main breaks."

Part of the city's solution for its water utility problems is an ongoing project to replace aging water lines.

The city's oldest lines are the cast-iron pipes installed in the 1950's. About nine miles of the 84 miles of 1950's pipe were replaced in April. Information on how many miles have been replaced since was unavailable.

The old pipes are being replaced with PVC pipes rated to last for about 100 years and do not burst as easily with temperature extremes, Salcido said.

That project has been hampered by high costs and insufficient funds.

"A very small percentage of the 1950's pipes have been replaced," he said.

According to the city's estimates, replacing the remaining cast-iron pipe will cost $58.2 million, or $773,000 per mile.

That process could take as long as 31 years at the current funding rate through water utility revenue.

The Public Works Department will present a water-rate study, by Red Oak Consulting, to City Council in the spring.

The last rate study was approved in 2006 and went on for five years.

It included five years of rate increases, Salcido said.

Red Oak Consulting is a division of Malcolm Pirnie, Inc., one of the country's largest environmental engineering and consulting firms. Malcolm Pirnie merged with ARCADIS, an international environmental consulting firm, in 2009.