Public Utilities
Unidirectional Flushing Program

For decades, Portsmouth has used a conventional citywide flushing program to maintain water quality. Conducted every spring, conventional flushing consists of opening hydrants in a specified neighborhood to flush out accumulated rust and sediment. While effective, this type of flushing does not increase the speed of water flow through the pipes enough to dislodge stubborn deposits.

Using new computer mapping technology, the Department of Public Utilities is developing a new unidirectional flushing program. Unidirectional flushing consists of closing approximate water system valves to create one way flow in a neighborhood water pipe loop and then opening hydrants in a set sequential manner. This increases the speed of the water flow in the pipes to six feet per second or higher. These high velocities produce a scouring action in the pipes, removing even the most stubborn deposits. This program is a good tool for use in Portsmouth, with its large inventory of older rusty pipes.

Unidirectional flushing uses up to 40% less water than conventional flushing, and allows for a better response to localized water quality complaints. Because of better sediment removal, the effects of unidirectional flushing last much longer. Additionally, unidirectional flushing will test almost all of the water system valves and hydrants, identifying those in need of repair or replacement.