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Water losses’ assessment in an urban water network Dídia I. C. Covas, Ana Cláudia Jacob, Helena M. Ramos Civil Engrg. Dept., Instituto Superior Técnico, Technical University of Lisbon (TULisbon), Av. Rovisco Pais, 1049-001 Lisbon, Portugal. E-mail: [email protected], [email protected] Abstract: This paper presents the assessment of real and apparent losses in a District Metering Area of a Portuguese water utility based on the analysis of collected minimum night flow data and extended period simulations of the system. The DMA covers a 0.7 km2 area, is predominantly domestic consumption, with 6200 inhabitants and a large non-domestic consumer; it is a temporarily DMA, isolated by closing ten boundary valves. It has 9.4 km of pipes with diameter from 50 to 300 mm, 589 service connections and 3400 billed consumers. Flow and pressure data have been collected at the DMA input section, during a leak detection survey carried out during an eight-weak period. A brief description of the leak detection survey is presented. Water losses have been assessed before and after the leakage detection survey by means of a bottom-up approach (a six-step procedure) based on minimum night flow analysis and dynamic hydraulic simulation of the system. Minimum night flow data, between 2:00 and 4:00, were used for estimating real losses. Daily leakage pattern has been estimated by means of hydraulic simulations of the system using EPANET. The analysis has shown that the leak detection survey reduced real losses in 27%, which corresponds to an annual water volume of 130 000 m3 (despite the seasonal demand variation of 22%) and apparent losses and unbilled authorised consumption, even after the survey, still represent 33% of total water volume. Keywords: Water losses; leakage; network; simulation; minimum night flow. INTRODUCTION Changing climatic conditions and high temperatures have led to shortages and water restrictions in many countries, simultaneously, with the increase of domestic and industrial demand, in the last twenty years; consequently, leakage reduction and control has become a high priority to water utilities and to the regulators. Every water distribution systems have leaks and ruptures as a result of high operating pressures, inadequate design, construction and operation, life cycle of pipes and infra-structures. Water losses may vary between 10 to 40% of the total water volume distributed, in developed countries, which can be of great economic importance. According to a study performed by 31 water distribution companies in the United Kingdom, almost 50% of water is unmeasured but consumed, 25% measured and consumed, and almost 23% is lost (WRC, 1994). Water losses have several associated costs: the direct costs of water lost, the cost of interrupting the supply and the cost of repairing the system, and the costs to the society associated to the interruption of supply (WRC, 1985; 1994; Lambert et al., 1998; Farley and Trow, 2003; Ferreira et al., 2006). Water input into the system has two main components – authorised consumption and water losses (Alegre et al., 2000). Water losses are the difference between the system input volume and authorised consumption (measured or estimated). Losses have two components (Alegre et al., 2000; Farley and Trow, 2003): real or physical losses that correspond to leaks and ruptures in transmission or distribution mains, storage tanks and service connections until the consumer meter, and apparent losses associated with customer and input metering inaccuracies (errors) and unaccounted for consumption. Real losses include leaks and ruptures. Leakage is water that is lost (undetected) continuously in the system due to the lack of tightness of pipe junctions, valves and other fittings and due to small cracks in pipes, and that is never used by the consumers. Flow rate associated with each leak is usually quite small, therefore leaks are not easily detected. Bursts and ruptures refer to sudden accidental bursts in pipes and fitting. Real losses depend greatly on normal operating pressures, burst frequencies, infra-structure age, construction processes, and rehabilitation strategies. Apparent losses include measurement errors (flow-meters), illegal connections and uncounted for uses (e.g., irrigation, street washing and fire fighting). These can be minimised by using more accurate measurement equipment, installing meters at uncounted for consumption sites (e.g., irrigated green spaces, council consumption) and regularly inspecting the system looking for illegal connections. Water Practice & Technology Vol 3 No 3 © IWA Publishing 2008 doi: 10.2166/WPT.2008061 This paper presents a methodology to carry out a bottom-up analysis for assessing water losses based on the analysis of minimum night flows as presented in Report F of WRC (1994) and the hydraulic simulation of the system by using EPANET. The proposed methodology is applied to a district metering area (DMA), of Lisbon water distribution system, namely as DMA320, using flow and pressure collected data during a leak detection survey carried during an eight week period. Water losses were assessed before and after the survey and conclusions are drawn concerning the benefit of the leak detection survey. CASE STUDY The water distribution system of Lisbon belongs to the water utility EPAL, S.A. (Empresa Portuguesa das Águas Livres, S.A.); the system has 1400 km of pipes, supplying directly a population of 700 000 inhabitants and conveying water to boundary Lisbon boroughs. DMA320 is one of the 128 district metering areas of Lisbon water distribution system, located in the high zone of the network (with elevations between 60-90 m). DMA320 covers a 0.7 km2 area in the council of S. Domingos de Benfica (Figure 1a), predominantly residential (mainly, domestic consumption), with approximately 6200 inhabitants and a large non-domestic consumer - the Zoo – that represents one- third of total billed consumption. DMA320 has been temporarily isolated by closing ten boundary valves. It has 9.4 km of pipes made of asbestos cement, cast and ductile iron and polyethylene, diameters from 50 to 300 mm, 589 service connections and 3400 consumers. The train line divides the council (and DMA320) in two main areas with urban characteristics completely different: the north zone (above the train line) and the south zone (below the train line). North zone covers 65% of the area, being 33% of the area occupied by the Lisbon Zoo; however, this zone is the most populated with 94% of the resident population, being, thus, a highly occupied urban area (Figure 1b). South Zone has buildings from the XX century, mainly non-residential, a College, a Church, a Palace and a large green area (Monsanto Park); there are no commercial areas in the zone (Figure 1c). Lumiar (a) Carnide Campo Grande North Zone N. S. de Fátima South Zone Benfica Campolide Boundaries of S. Domingos de Benfica Train line Limit of DMA 320 (b) (c) Figure 1. (a) Map of S. Domingos de Benfica DMA320. Photos of (b) North Zone and (c) South Zone 2 LEAK DETECTION SURVEY Most DMAs in Lisbon water distribution system are temporary, created by the closure of valves during the period of the survey. Typically, a leak detection survey has duration of three weeks and overlaps in the first and in the last week with two other surveys; thus, there are approximately 50 surveys per year and each DMA is checked every three years. The first week is used for the preliminary works: closure of valves, installation of measurement equipment and installation of leak noise detectors. A digital flow meter and pressure transducer are installed at the input section of the DMA, and connected to a data logger (Figure 2a). The two following weeks are used for the leak detection and location. Maximum night pressures and minimum flows are monitored to continuously assess the progress of the survey and estimate leakage reduction. Leak pre-location is done by using an acoustic leak detection system, composed of a number of acoustic noise loggers and a leak seeker (Figure 3). Acoustic noise loggers are installed at available pipe- fittings (fire hydrants, valves and scours), spread all over the DMA. Every day, the survey team drives along all installed loggers with a leak seeker that reads minimum noise registered during the last 24 h in each installed logger. The seeker provides on-site information of the leakage situation (leak or no-leak) in each logger. Comparison of recorded noise levels between loggers provides information about which loggers are located closest to the leaks. Once identified the area of the DMA with a leak, other leak locations techniques are necessary to pinpoint the accurate position of the leak. Usually leaks are located in valves or fire hydrants. Examples of two equipments used are the leak noise correlator, the acoustic stethoscope, the listening stick and the ground microphone (Figure 3). Figure 2. (a) Pressure and flow meters installed and datalogger. (b) Acoustic leak detection system Figure 3. Leak listening system: acoustic correlator, stethoscope, listening stick and ground microphone DATA COLLECTION Flow and pressure data have been collected in the DMA320 input section, during an atypical survey eight- week measurement survey carried out during from 13th October to 13th December 2004; this was because the DMA was known to have a high volume of non-revenue water as high as billed consumption. Data were collected every 2 minutes (i.e., with a frequency of 30 measurements per hour) – see data collected in the first week in Figure 4a. A flow meter was installed at the inlet of the largest consumer of the DMA (the Lisbon Zoo) during the fifth week. This consumer showed a high variation of daily consumption with two peak flows at 9:30 a.m. and 3:30 p.m., and other random extremely high peak flows, and a constant night consumption.

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