However, perfection in design is frequently compromised by cost, especially in poor and developing communities. Good design of plumbing systems is an important step in ensuring that the installations are efficient, safe and affordable. It should take into account the special needs and limitations of developing countries and should also ensure that the installations are appropriate for the different situations they serve. An understanding of the technical requirements and regulatory restrictions is vital for the provision of good plumbing services. This chapter includes design recommendations for plumbing installations in single dwellings, multiple dwellings and multi-storey build- ings. It deals with special issues related to industrial and other special purposes, hot water and other dual supply systems and storm water drainage. It includes guidelines on capa cities of plumbing systems, plumbing materials and products, and the use of protective devices to prevent backsiphonage and backflow.

For plumbing purposes, the term “multi-storey” is applied to buildings that are too tall to be supplied throughout by the normal pressure in the public water mains. These build- ings have particular needs in the design of their sanitary drainage and venting systems. Water main supply pressures of 8–12 metres (25– 40 feet) can supply a typical two-sto- rey building, but higher buildings may need pressure booster systems. In hilly areas, the drinking-water supply pressures will vary depending on the ground elevation. In these cases, the water authority may have to specify areas where particular supply pressures can be relied upon for the design and operation of buildings. Where a building of three or more storeys is proposed a certificate should be obtained from the drinking-water supply authority guaranteeing that the present and future public drinking-water supply pressure will be adequate to serve the building. If the public water pressure is inadequate, suit- able means shall be provided within the building to boost the water pressure.