AUSTIN (KXAN) – For three years running, Austin Water Utility has posted an increase in the amount of water leaked from city pipes, and utility officials have not pinpointed exactly why.

The city’s latest water loss report shows more than 5.8 billion gallons of treated drinking water seeped from city pipes before reaching customers in 2015-a 23 percent increase over the previous year, according to annual water loss audits submitted to the Texas Water Development Board.

“We have not identified or pinpointed why we would have an increase in a year over year [leaks],” said Rick Coronado, assistant director of pipeline operations with the utility. “Looking at the last three years, we have seen a trend of increase.”

Coronado is referring to “real” losses, a term for actual drinking water lost from city pipes. The city separately tracks accounting losses due to meter inaccuracy. Austin Water estimated the cost of the 2015 “real” losses at $2.35 million. Overall, the amount of drinking water lost from city pipes has nearly doubled since October of 2011, audits show.

Coronado said the utility has crews working year-round to fix broken pipes in a timely manner, and the utility is looking at new strategies to contain leaks. He also said the city’s “leakage index,” which is an industry benchmark based on a range measures including the length of pipes and pipeline pressure, is still within a good range.

“Austin has about 750 miles of old cast iron pipe that is at, or over, its rated life,” Robbins said. “Maybe this is finally catching up to us.”

To put 5.8 billion gallons into perspective, it is enough to fill Lady Bird Lake nearly two and a half times. The entire City of Austin used about 128 million gallons of water on Thursday, May 12, according to city and TWDB data.

And while water leaks steadily increased over the past three years, so have water rates for utility customers. Spokesperson Jason Hill said the utility could not estimate exactly how much the water leaks impact customer bills.

Longtime local environmentalist and utility critic Paul Robbins said the utility does appear to have an issue with leaks, but “they don’t know exactly why.” Perhaps the problem could be attributed to aging pipes, he said.

“Austin has about 750 miles of old cast iron pipe that is at, or over, its rated life,” Robbins said. “Maybe this is finally catching up to us.”

Austin Water Leaks

KXAN reported on the city’s plan to replace that cast iron pipe, which could take roughly 75 to 100 years at the current pace. Coronado said the cast iron pipe replacement program, called Renew Austin, is ongoing. The city is also replacing problematic service lines, he added, which branch off water mains to customer meters, he added.

A relatively small portion of the increase in leaked water could be attributed to a break in a single 66-inch wide East Austin transmission main. In 2015, Hill said that huge pipe leaked more than 105 million gallons.

When it comes to leaks, the utility also faces unique challenges in Austin. “We are in a very highly active construction development time frame,” Coronado said.

Construction projects carry with them a risk of hitting water mains and causing leaks.

Pipe leaks can also be difficult to detect. If water from a broken pipe comes to the surface, the break can be relatively easy to isolate. If a pipe is broken deep underground, and the water never reaches the surface, it can be much more difficult to find and repair, Coronado said.

The water loss audit compiled by AWU is sent to the Texas Water Development Board, which calculates a water loss threshold.

According to a TWDB official, AWU has broken that threshold in the past year. That means, if the utility seeks financial assistance for a water project from TWDB, the utility would need to include funds to address the water loss or request a waiver.

Austin City Council voted in late April to allow city staff to apply for more than $80 million in funding from the State Water Implementation Fund of Texas, which is managed by TWDB, for smart water meters.