Every day, the Philadelphia Water Department sends 256 million gallons of treated drinking water through 3,000 miles of water mains.

A $2 million grant announced yesterday will help further ensure its safety, city and federal officials said.

The grant - which is actually $9.5 million, but depends on future budgets for the U.S. Environmental Protection Agency - will help fund improvements in a system to help detect and prevent a terrorist attack or other intentional contamination.

The grant is part of an EPA water-security initiative that began in 2005 with a pilot program in Cincinnati.

Now, the pilot is being expanded to four major cities - Philadelphia, San Francisco, Dallas and New York.

"We've always known we have great water," Mayor Nutter said during a ceremony in which he accepted an oversized $2 million check.

Now, he said, the city will serve as a model for developing a contamination-warning system.

Acting EPA regional administrator William Wisniewski said the new national program was a "progressive" step beyond the standards of the Safe Drinking Water Act.

City Water Commissioner Bernard Brunwasser said the program would complement an early-warning system for the city's water supply. It alerts downstream water users on the Schuylkill and the Delaware River to any potential water-quality problems.

Implemented in 2005, the system has logged 100 "events," including a 100-million-gallon fly ash spill on the Delaware River in August 2005 and a cyanide discharge into Wissahickon Creek in June 2006. Flood warnings and sewage discharges were also logged.

While that addresses water entering the treatment plants, the new security initiative is intended to protect water after it leaves the plants.

Officials said they planned to look for more compounds and increase the number of monitors now at 19 locations within the water main network. At each site, sensors now track parameters, such as chlorine, pH, and turbidity.

Radical changes could signal a problem - from a broken pipe to intentional contamination.

Alexa Obolensky, the Water Department's laboratory research supervisor, said the grant would both help to prevent the extreme case of a terrorist attack and improve daily Water Department operations.

Officials also intend to develop new ways to use and interpret the information to determine whether a threat actually exists. "We don't want false positives, or false negatives," Obolensky said.

In addition, the plan calls for better mapping systems so workers can look at whether changes in water data coincide with, say, work on a water main, or an increase in customer complaints about water quality.

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com.