Water Main Breaks

Fact Sheet

When the temperature drops in Prince George’s and Montgomery counties, the chances of water main breaks rises about 60% compared to warmer months. Break can leave hundreds of people without service and can also cause serious traffic problems, so WSSC takes winter preparations very seriously. WSSC has teams of skilled contractors on standby, along with trucks, heavy equipment, and the latest technology ready to roll for the coldest season.

Water Mains

  • Serving a 1,000-square-mile area, WSSC maintains more than 5,500 miles of water mains -- enough pipe to stretch from Washington, D.C. to California and back! And we’re replacing more than 60 miles of pipe each year.
  • The water mains range in size from 1 inch to 96 inches (8 feet) in diameter.
  • Since 1977, WSSC has used ductile iron pipes.
  • Ductile iron pipes are stronger than cast iron, pre-lined with cement mortar and are not brittle.
  • The most common size for a water main is 8 inches, followed by 6, 12, 10 and 16 inches.

How Temperature Impacts Water Mains

There is a relationship between water temperature and breaks. A sudden temperature drop provides a kind of shock to the pipes. Most of WSSC water comes from the Potomac River which feeds the WSSC Potomac Water Filtration Plan, and when air temperatures drop the water in the Potomac River drops too. It takes a day or two, but an increase in breaks and leaks soon follow. The river also brings the colder water from higher elevations to the west. Even a 10-degree change in the air or water temperature can dramatically increase stress on a pipe, including underground pipes. Water temperature below 40 degrees F can also cause pipes to become more brittle, and above ground pipes can freeze when the air temperature hits freezing or below. That leads to increased external stress. The Patuxent River, and the two reservoirs formed behind Brighton and T. Howard Duckett dams, provide about 30% of the water for WSSC customers via the Patuxent Water Filtration Plant. But the reservoirs are deeper than the Potomac River, and the temperatures don’t change as fast. Therefore we have fewer breaks and leaks in areas served by the Patuxent Plant.

Other Factors That Contribute To Breaks

  • Material: Of the 5,500+ miles of water mains in our distribution system, approximately 2,900 miles are cast iron pipe (16-inch diameter and less), which were used from 1916 to through 1976. These pipes are prone to breaks because cast iron is a brittle material and is very sensitive to external pressure placed on the pipe.
  • Soil Erosion: A previous pipeline break, excavation or nearby construction activity often erodes soil around water mains, which can cause breaks.
  • Corrosion: Older pipes are not cement lined and corrode inside and outside, increasing the chances of a break.
  • Pipe Diameter: The smaller the pipe’s diameter, the greater the risk of breakage.
  • Age: The break rate for pipes increases after 60 years. Age alone, however, cannot always be used as an indicator of failure. Some pipes installed in the early 1900s have never broken.
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