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Public Health Engineering


The public health engineering sector is responsible for the Collection of water, purification, transmission and distribution of water. A Public Health Engineerr has to perform his job by calculating design flow, design population , design area and population density

  1. Collection of water

  2. Purification works

  3. Transmission works

  4. Distribution works

Water works Explained

  1. Collection of water:
    This includes the collection of water from all available sources to ensure continuous supply of water to the community.
  2. Purification works:
    Quality of the collected water is checked by physical and chemical tests on water and if the quantity is not satisfactory and according to WHO standards then, purification or treatment of water is done to make it suitable for its intended use e.g. cooking, drinking, bathing, washing etc.
  3. Transmission works:
    Transmission works includes measure taken to ensure the purified supply of water by laying out conduits, which do not affect the quality of water
  4. Distribution works:
    Water is then distributed to the consumers in desired quantity at adequate pressure. The quantity of water may be different for residential, commercial and industrial zones. So accordingly, there should be a difference between the quantities of water that they will receive and hence the transmission works.Similarly, the pressure of water is also important in industries, storied buildings, and hilly areas.

Design population:

It is the no. of people for whom the project is designed. The population should be considered as it would be at the end of design period.

Design Flows:

The maximum discharge required at the end of transmission system is called design flow.
Per capita consumption is the average intake of water per person. It may be for a single day, a week, a month or annually. It can be found out by dividing the total consumption of water by the number of individuals in population using that water. The flow of water for design is calculated by multiplying the average per capita consumption annually with the design period (in years) and the design population.

Design period:

It is the number of years in future for which the excess capacity is provided. For this amount of time the proposed system, its component structures and equipments should be appropriate and adequate.
The design period depends upon:

  • Life of components system structures used.
  • Ease of expansion of the project
  • The type of technology used
  • The rate of increase of population
  • The rate of increase in water demand.

The flow required for design period must be estimated and not over-estimated, to prevent the project from becoming un-economical and over-burdening the community with extra cost.


Population density

The number of persons per unit area – e.g. persons/Km2



Average city

30 – 40 /Acre

Sparsely built up residential area

15 /Acre

Closely built up residential area

35 /Acre

Apartments and tenement districts

100 - 1000 /Acre

Table 1 - Densities of different areas

Keywords: asic design flow, design flow, sanitary sewer design flows, sewer design flows, wastewater design flows, design periods, interior design periods, periods of design, design periods timeline


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