Acoustic Fiber Optic Monitoring System

WSSC Water has the longest active AFO system in the United States

In 2007, How AFO Works. Prestressed Concrete Cylinder Pipe (PCCP) comprises concrete, reinforcing steel wires, and steel. The Acoustic Fiber Optic (AFO) cable floats inside PCCP and listens to "ping" of wire breaks. When AFO hears a "ping," the data is recorded and sent to WSSC Water. WSSC Water began installing Acoustic Fiber Optic (AFO) cables to detect the sounds associated with pre-stressed wire breaks on prestressed concrete cylinder pipe (PCCP) sections while the pipelines are in service. Once installed, the AFO system continuously monitors the integrity of all the pipes and provides notification to trained personnel if a potential problem is detected in any pipe section.

WSSC Water has a total 145 miles of PCCP ranging from 36 – 96 inches. As of 2026, 110 miles of WSSC Water’s PCCP is monitored with AFO, making it the longest, active monitoring system in the United States. The Commission also conducts planned inspections. PCCP ranging from 48 – 96 inches is inspected every 5-6 years. Pipe that is 36 – 48 inches is inspected every 7-8 years.

Because the design of the pipe, AFO is effective only for PCCP, not for other types of pipe in the system such as ductile iron or cast iron.

Pings Protect Pipes. WSSC Water has the longest active AFO monitoring system in the country. Total miles of pipe monitored by AFO: 110 miles. AFO has avoided 74 costly emergency repairs, saving WSSC Water customers approximately $248 million

Last Modified: September 28, 2026, 9:58 am EDT