Water Main

Published: | Updated: May 14, 2021

Definition - What does Water Main mean?

A water main is a primary underground pipe in a municipal water distribution system. It is a major artery that supplies water to smaller pipes on the way to homes and businesses. Water mains take clean water from a city’s water treatment plant to communities that need it and is, therefore, a critical part of a nation’s utility infrastructure. The pipes transport a high volume of water under pressure to neighborhoods that are depending on water mains to bring them clean water from the city's water treatment facility.

Water mains can be subject to various wear and tear issues including tuberculation, faulty joints, inadequate hydraulic capacity, and corrosion. Water mains have been flagged as critical issues in aging utility infrastructures in developed countries.

An old water main, especially galvanized iron exposed to groundwater containing iron and manganese can cause a build-up of hardened scale inside the pipe. This not only changes the color, odor, and taste of the water, it also reduces its flow velocity and capacity.

Old water mains made from cast iron can be brittle and often crack due to their inability to expand and contract with temperature changes. These pipes are now being replaced with ductile iron or plastic pipes like high-density polyethylene (HDPE) and polyvinyl chloride (PVC) that are flexible, and resistant to corrosion and abrasion.

Trenchless techniques have been very successful in the rehabilitation of older water main pipes. Trenchless technology has been effectively applied to the rehabilitation of water main pipes by use of cured-in-place pipes, sliplining, robotic pipe repair, and more. Pipe rehabilitation often involves the sliplining of HDPE pipes rather than replacement, and water main renewal costs the U.S. over $1 billion per year.

Trenchlesspedia explains Water Main

Water mains carry potable water from water pumping stations to homes, businesses, schools, and industries. Regular maintenance of water mains is necessary to remove sediments and maintain the quality of water. The buildup of scale from calcium, iron, and manganese inside the pipe interferes with its flow capacity and also affects the taste and quality of water.

Pipe Materials Used for Water Mains

Different types of materials are used for the manufacture of water mains and fittings depending on soil types and pressure levels. Pipes are made of metal such as cast iron, ductile iron, steel and copper, vitrified clay (VCP), reinforced concrete, asbestos cement, HDPE, PVC, and fiberglass.

Water main diameters range from 6 to 16 inches while branches or laterals to homes and businesses range in diameter from ½ an inch to 6 inches. A pipe’s structural strength and pressure rating is defined by its wall thickness and is expressed as a ratio of the wall thickness to the pipe’s diameter.

Gravity or Force Mains

There are two types of water distribution systems – gravity or force mains. Gravity systems rely on gravity for the water to flow while force mains rely on applied pressure heads induced by pumps. Force mains are smaller than gravity systems as the induced pressure can cause high-flow velocities even in small diameter pipes.

The pressure is also derived directly from the difference in elevation between the elevated overhead water tank and the user. Gravity is involved here but this is not considered a gravity system as water had to be first pumped up to the tank.

Causes of Damage to Water Mains

Water mains can be damaged anywhere due to several reasons:

· Unintentional hit during excavation work.

· Aging pipe material.

· Changes in pressure due to thermal expansion or water hammer.

· Ground settlement.

· Corrosive soils.

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