6.2. Pipes

A water pipe is any pipe or tube designed to transport treated drinking water to consumers. The varieties 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. Materials commonly used to construct water pipes include cast iron, polyvinyl chloride (PVC), copper, steel or concrete.

Photograph 6.1. Construction of pipes

Photograph 6.1. Construction of pipes

For many centuries, lead was the favored material for water pipes, because its malleability made it practical to work into shape (this use was so common that the word "plumbing" derives from the Latin word for lead). This was a source of lead-related health problems in the years before the health hazards of ingesting lead were fully understood; among these were stillbirths and high rates of infant mortality. Lead water pipes were still in common use in the early 20th century and remain in many households. Lead-tin alloy solder was commonly used to join copper pipes, but modern practice uses tin-antimony alloy solder to join copper in order to eliminate lead hazards. 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 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.

Types of Pipes

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, galvanized iron pipes and cast iron pipes. Cement pipes include concrete cement pipes and asbestos cement pipes. Plastic pipes include plasticized polyvinyl chloride (PVC) pipes.

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.

Galvanized Steel or Iron Pipes

Galvanized 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 galvanized steel or iron as a conveyer for drinking water is problematic where water flow is slow or static for periods because it causes rust from internal corrosion. Galvanized steel or iron piping may also give an unpalatable taste and smell to the water conveyed under corrosive conditions.

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.

Plasticized 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. However, they are prone to physical damage if exposed above ground 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.

Cost Considerations 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:

1. Weight of the pipe: A lightweight pipe can be handled easier and faster.
2. Ease of assembling: Push-on joints can be assembled much faster than bolted joints.
3. 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.

Health Aspects 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. 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 minimizing 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. Inflows of contaminated water during distribution are major sources of waterborne pathogens and thus cause of waterborne diseases. 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 1,300 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.

Applicability Water pipes are required almost everywhere, especially for drinking water distribution. The most robust and durable type of water pipes is probably made from cement. Due to their heavy weight they are however difficult and expensive to install. PVC pipes are easier to install and much lighter, and thus particularly suited for remote areas that are difficult to access.