Water Distribution Pipes

A water pipe is any pipe or tube designed to transport drinking water to consumers. If the water is treated before distribution or at the point of use (POU) depends on the context. In well planned and designed water distribution networks, water is generally treated before distribution and sometimes also chlorinated, in order to prevent recontamination on the way to the end user. The varieties of water pipes include large diameter main pipes, which supply entire towns, smaller branch lines that supply a street or group of buildings, or small diameter pipes located within individual buildings. Water pipes can range in size from giant mains of up to 3.65 m in diameter to small 12.7 mm pipes used to feed individual outlets within a building. Materials commonly used to construct water pipes include polyvinyl chloride (PVC), cast iron, copper, steel and in older systems concrete or fired clay. Joining individual water pipe lengths to make up extended runs is possible with flange, nipple, compression or soldered joints (SCOTT 2011).

Pipes come in several types and sizes. They can be divided into three main categories: metallic pipes, cement pipes and plastic pipes. Metallic pipes include steel pipes, galvanised iron pipes and cast iron pipes. Cement pipes include concrete cement pipes and asbestos cement pipes. Plastic pipes include plasticised polyvinyl chloride (PVC) pipes (LEE n.y.).

Steel pipes

Steel pipes are comparatively expensive, but they are the strongest and most durable of all water supply pipes. They can withstand high water pressure, come in convenient (longer) lengths than most other pipes and thus incur lower installation/transportation costs. They can also be easily welded (LEE n.y.).

Galvanised steel or iron pipes

Galvanised steel or iron is the traditional piping material in the plumbing industry for the conveyance of water and wastewater. Although still used throughout the world, its popularity is declining. The use of galvanised steel or iron as a conveyer for drinking water is problematic where water flow is slow or static for periods of time because it causes rust from internal corrosion. Galvanised steel or iron piping may also give an unpalatable taste and smell to the water conveyed under corrosive conditions (WHO 2006).

Cast iron pipes

Cast iron pipes are quite stable and well suited for high water pressure. However, cast iron pipes are heavy, which makes them unsuitable for inaccessible places due to transportation problems. In addition, due to their weight they generally come in short lengths increasing costs for layout and jointing.

Concrete cement and asbestos cement pipes

Concrete cement pipes are expensive but non-corrosive by nature. Their advantage is that they are extremely strong and durable. However, being bulky and heavy, they are harder and more costly to handle, install and transport (LEE n.y.).

Plasticised polyvinyl chloride (PVC) pipes

PVC pipes are non-corrosive, extremely light and thus easy to handle and transport. Still, they are strong and come in long lengths that lower installation/transportation costs (LEE n.y.). However, they are prone to physical damage if exposed overground and become brittle when exposed to ultraviolet light. In addition to the problems associated with the expansion and contraction of PVC, the material will soften and deform if exposed to temperatures over 65 °C (WHO 2006).

(Adapted from CHRISTENSEN 2005)

Installation costs make up a major part of the total cost of a project. Differences in the cost of the actual pipe do not change the total cost of the project much. However the following factors should be considered concerning installation costs and the choice of pipe:

• Weight of the pipe: A pipe that is lightweight can be handled easier and faster.
• Ease of assembling: Push-on joints can be assembled much faster than bolted joints.
• Pipe strength: If one type of pipe requires special bedding to withstand external pressures while another pipe does not, the choice can impact installation costs significantly.

A leaking distribution system increases the likelihood of safe water leaving the source or treatment facility becoming contaminated before reaching the consumer. Moreover, leaking can result in considerable water loss on the way to the end-user (also see the factsheet on leakage control). The distribution system must be designed, managed and maintained to guarantee a minimal level of leakage. The internal pipe pressure constantly must be greater than the external hydrostatic pressure. This will ensure the delivery of the water reducing loss from leaks and minimising excess growth of pathogenic microorganisms. A certain level of free residual chlorine or chloramine disinfectant will reduce the risks of recontamination within the distribution system (see also chlorination). Inflows of contaminated water during distribution are major sources of waterborne pathogens and thus cause of waterborne diseases (WHO 2006).

Water pipes are often made of copper and bath fixtures may be made from alloys containing copper (brass, bronze). The U.S. Environmental Protection Agency (EPA) has established a Maximum Contaminant Level Goal (MCLG) for copper in public drinking water systems at 1300 parts per billion (ppb). MCLGs are non-enforceable health standards for drinking water. The principal source of copper in drinking water results from the leaching of copper from pipes and bath fixtures due to corrosive (acidic) water. The blue-green stain left in some bath fixtures is a sign of the presence of copper in water. Usually, excess copper in drinking water comes from the leaching of the plumbing system into the water that has been sitting in the pipes for several hours. Therefore, letting the water run for 30 to 60 seconds before using it for drinking or cooking will often significantly reduce copper levels (DES 2005).