Dissemination and training
Chapter 1 Introduction and objectives
1.2 Water supply in urban areas
1.2.2 Water supply network
The drinking water transport system and distribution network or water supply network is the infrastructure required to transport water from the drinking water treatment plant to the consumption point. The core elements of the network are summarized in Table 1.1 and the necessary equipment in Table 1.2. As can be observed, this network involves the construction of necessary infrastructures whose characteristics will depend greatly on each specific case. Thus, the description of the elements below might not apply to certain networks but is adequate for providing common terminology to be used in this dissertation.
Elements of the network
Drinking water in the network is always pressurised, and must have enough pressure to reach the consumption point. Although this pressure can be achieved by gravity if there is sufficient slope, pumping is usually needed. Indeed, the operation of water supply networks is characterised by the electricity consumption required for pumping (Venkatesh and Brattebø 2011a). Regarding maintenance, some operations such as an internal coating of the pipes, rehabilitation, replacement of smaller parts of a pipeline, repair and inspection are sometimes required (Venkatesh and Brattebø 2012a).
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Table 1.1 Description of the main elements in the water supply network.
Element* Description and Observations
Transport network The primary section of the supply network, usually from the first water tank after the treatment plant* until the secondary water tank before the distribution system.
This section of the network has wider pipes and is typically made of strong materials such as reinforced concrete or ductile iron (depends on the conditions and customs of the region).
Distribution network Section of the supply network from the secondary water tank until the connection to households.
This section is longer due to the capillarity of the network and the pipes hold smaller diameters. Pipes are usually made of polyethylene, PVC or steel.
Water supply tank The facility used to store drinking water. Municipal water tanks usually hold large volumes of water (hundreds of cubic meters) and are generally made of reinforced concrete or steel.
Usually, there is another water tank before water reaches households in an urban area. There can be more tanks in the transport or the distribution network for flow regulation, pressure regulation and supply security
*Water extraction and treatment have not been excluded because they are before the water supply network, and thus out of the scope of the dissertation.
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Table 1.2 Description of the main equipment of the water supply network.
Element Description and Observations
Pipe and appurtenances The basic infrastructure of the network made up of a tubular section for water conveyance. It can be made of different materials such as plastics (PVC, HDPE), iron or concrete.
Pipes usually require certain appurtenances such as joints or additional pieces for proper functioning.
Trench or ditch section Section excavated in the ground for the installation of pipes.
The ditch is backfilled with gravel, sand or other materials that protect the pipe.
Pumping station Facility for pumping water through the network. It includes pumps and the necessary equipment.
Valve
Devices along the network that regulates the flow of water opening, closing or partially limiting the flow.
There are different types depending on their function. For instance, valves can be used for pressure reduction or backflow prevention.
Hydrant Connections for the provision of water located along the distribution network.
Metering Flow meters are installed at key points of the network for the measurement of the water flow. At least, water is measured at the beginning of the first water tank and the entrance of households.
12 Operation of the network
The network normally has (particularly old networks) significant leakages because it is pressurised. It is well known in engineering that higher pressure in the network implies more likelihood of water leaks (Garcia and Thomas 2001). In Europe, estimates show that water loss through leakages can range between 5% and 50% (particularly in old networks) depending on the country (European Environmental Agency 2008). For this reason, this is a major concern in water management strategies, provided it increases the overall economic and environmental costs of water supply.
There is extensive scientific literature analysing different methods for the reduction of water loss due to leakages. Various methods are proposed such as effective detection of leakages using smart metering (Britton et al. 2013), predictive maintenance (Tsakiris et al. 2011), strategical pipe replacements (Creaco and Pezzinga 2015) or optimisation of valves control (Vairavamoorthy and Lumbers 1998). As a result of the increasing interest, the European Commission launched a reference document for good practices on leakage management on 2015 (European Comission 2015).
The administration of the water supply network is affected by the European Council Directive on the quality of water intended for human consumption (Council Directive 98/83/EC) (EC 1998) as well as by the Council Directive for a Community action in the field of water policy (Council Directive 2000/60/EC) (EC 2000). In Spain, these directives were transposed into the Royal Decree 140/2003 (Presidencia 2003) on sanitary criteria of water quality for human consumption and into the Royal Legislative Decree 1/2001 (MMA 2001) on water issues. In Catalonia, the water supply network is affected by the Legislative Decree on water issues 3/2003 (Departament de la Presidència 2003).
Environmental impacts of water supply
From an environmental perspective, the water transport and distribution network represents a significant contribution to the total environmental burdens of the urban water cycle. A study from Amores et al. (2013b) concluded that the water supply network accounted for between 20 and 40% in 7 out of 9 impact categories. The results from another study by Lemos et al. (2013a) showed that the supply network accounts for around 20% of the total UWC impacts, also in 7 out of 9 impact categories. One of the main contributions to these environmental impacts is the operating of the network, due to the energy consumption from pumping water. The electricity requirements can vary widely depending on the specific case, from low (250 kWh/MG) to high (1,200 kWh/MG) (Griffiths-Sattenspiel et al. 2009). The leakages of the network would increase these energy requirements (and hence the environmental impacts) because more pumping is required to maintain the adequate pressure.
In this context, the environmental assessment of water supply networks has the potential to reduce environmental impacts from the UWC. This assessment should reveal which factors of the materials, construction, use and maintenance of networks are crucial to improve the environmental performance.
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