Environmental Engineering Reference
In-Depth Information
8.1
INTRODUCTION
Water distribution networks will be designed to provide satisfactory level of service under
regular conditions, and also in number of irregular supply scenarios. This additional safety
factor comes at additional costs that should be paid for investments and/or operational
measures with the highest effect for the service levels. The least cost design should in theory
be the least reliable, but this conclusion cannot be analysed from the perspective of asset
value alone, because the operational costs and repayment of loans can participate
significantly in the cost of water supply. Thus, how much is worthwhile to invest into
additional safety and what would be the impact on the service levels is a complex question.
Others
Connections
Transport and Distribution
Treatment
Extraction
Figure 8.1
Proportion of value of Dutch water supply assets (VEWIN, 1990)
Distribution network is the most expensive part of any water supply system asset. Figure 8.1
shows the value of assets of Dutch water supply assessed in 1988 at approximately five
billion US$, in which it can be seen that transportation and distribution component account
for over 50% of the total value (VEWIN, 1990). Similar proportion will be found in any other
country or particular drinking water system.
On the other hand, energy input in operation of distribution networks can also be very high.
This will depend on water extraction but in extreme topographic conditions of zone supply,
even more on water distribution. Belgrade Waterworks and Sewerage (BWS) estimated the
average consumption of electric energy of 0.86 kWh per m
3
of produced water, which in
2007 was approximately 211 million m
3
for the city of Belgrade in Serbia (Cvjetković, 2008).
This includes the costs of pumping from deep wells and also the drainage pumping stations,
in the city of 1.5 million inhabitants and distribution network located over five pressure zones
maintained by 28 drinking water pumping stations. Hence, the annual electricity bill of the
company is in the order of millions of US$.
This participates around 5% in the total annual costs of the company, as shown in Figure 8.2.
The total operational costs are estimated at 13% while the maintenance and materials occupy
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