Carriage of water from source of supply of raw water to the purification Water Treatment Plant(WTP) and then from WTP to the consumer, is known as Transmission System. It can be by means of open drains, canals, conduits and pipes of various sizes, different kinds as well as materials depending upon the requirements and hydraulics.
In order to carry raw water to WTP, it can be by means of drains or canals depending upon various factors such as hydraulic considerations and requirements. It can be transmitted by conduits or pipes as well. If the canals are open, there will be losses in the system, such losses being evaporation losses, frictional losses etc. etc. Further these open systems are subjected to theft of water and also can be polluted when passing through congested areas. Whereas when raw water is carried by means of pipes or conduits there will almost no evaporation losses but frictional losses will increase to a great extent.
Filtered water from WTPs or from intermediate booster pumping stations is transmitted and conveyed to the consumers by means pipe lines. Pipes are of different sizes from 10 mm dia to bigger sizes, even up to 2000 mm dia. These are of different materials such as PVC, G.I., D.I., C.I, PSC, M.S. etc. For smaller sizes in the distribution system, pipes of PVC and G.I are used. For bigger sizes, pipes of C.I. D.I., PSC and M.S. etc are used.
Sizes as well as quality of pipes are decided after considering the hydraulic requirements, losses, head of water at the consumer end, topography of the area, alignment and definitely financial as well as economic considerations.