Systems Analysis of Zaragoza Urban Water - SWITCH - Managing ...

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Systems Analysis of Zaragoza UWS Guillermo Penagos network. There are online meters at most facilities, but there is no data base. Therefore it is not possible to differentiate actual leakages at the distribution network from other factors contributing to unaccounted water, which has been reducing during the last decade, but still continues to be considerably high. In 2002, starting point of the water supply improvement plan, unaccounted water was as high as 34 million m 3 a year, nearly 45% of total withdrawal. Municipality estimated by that time approximately 17 million m 3 to be actual leakage in the distribution system, but this is just a rough estimation. In 2006 unaccounted water was around 32% of total withdrawal (see table 2). The goal is to reduce it below 15%. The main demonstration activity for Zaragoza within SWITCH project is to carry out a complete water balance for one sector of the city in order to improve the current knowledge about water consumption and leakage in order to reduce the percentage of unaccounted water. 4.2.4 Water use As it can be seen in figure 2, domestic use accounts for approximately the 62% of metered consumption. Industrial activities represent the 36% and public facilities plus landscaping consume only 2%. Data concerning water withdrawal and water consumption from 1997 –when campaigns for rationalizing water use at households and industries started– to 2006 are shown in table 2. Along this period water withdrawal has been reduced by 20 million m 3 year -1 due to both consumption reduction and infrastructure upgrading. Along the last decade domestic consumption has gone down from 140 to 110 l person -1 day -1 , leading to 6 million m 3 year -1 less withdrawal; even with population increasing with around 50 thousand people during the same period. Thus infrastructure upgrading accounts for 14 million m 3 year -1 reduction. 28
Systems Analysis of Zaragoza UWS Guillermo Penagos Table 2. Evolution of water withdrawal and consumption in Zaragoza Year Withdrawal (million m 3 per year) Population (thousand inh) Average consumption (l person -1 day -1 ) Metered consumption (million m 3 /year) Unaccounted tap water (%) 1997 84.7 601.6 139.8 39.9 45.6 1998 80.2 606.0 132.2 41.5 43.0 1999 80.4 607.3 132.2 41.2 43.2 2000 79.3 608.1 129.4 41.8 41.2 2001 79.7 613.4 128.8 42.5 39.0 2002 74.5 622.6 124.6 42.7 39.9 2003 71.7 628.4 122.4 44.1 38.2 2004 70.8 641.6 123.3 44.3 37.4 2005 68.2 650.6 118.0 44.6 35.0 2006 64.1 657.0 110.0 43.1 32.8 In spite of the important contribution of domestic water savings to the overall reduction of Zaragoza water withdrawal, municipality assumes that households are the major contributor to tap water loses since all over the city there are about 7000 to 7500 drinking water storage tanks installed between 30 to 40 years ago at the basement of buildings with the aim to assure continuous availability of water. At that time shortages were relatively common. Nowadays Zaragoza municipality considers such facilities not just unnecessary -since shortages have became very unusual- but also a source of problems since these tanks are poorly or even not maintained at all. There are three sustainability issues concerning these tanks: • Energy losses. By definition these facilities break the pressure existing in the pipeline –which would be enough otherwise to bring water up to the top of the building– making necessary for the building to consume electricity in order to pump water up. • Water losses. Municipality considers these tanks as the main source for water losses since poor maintenance may leave to continuous overflows that are discharged into the sewers (figure 5), mostly during low demand time (night time and holydays). Such losses become part of unaccounted water since meters are located at the outflow of the tanks (figure 5). • Public health. Legionella, Mycobacterium, enteric Amoebas as well as other opportunistic pathogens and nuisance organisms, some of these largely resistant to chlorine, may multiply inside these tanks when residence time increases (WHO, 2004). Due to these problems Zaragoza Municipality wants the tanks to be taken out of work, which they cannot do directly since those are private facilities. Municipality is considering to carry out campaigns to inform people about the disadvantages of such 29
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