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

Systems Analysis of Zaragoza UWS
Guillermo Penagos
4.2.1 Water inputs
4.2.1.1 Tap water source
Tap water source which is the Ebro river diverted 110 km upstream from Zaragoza
by “Canal Imperial de Aragon”. Ebro river discharge strongly fluctuates on a seasonal
basis, being as high as 500 m 3 s -1 in March and as low as 30 m 3 s -1 in August.
Quantity is sufficient to supply the city all over the year because the river is largely
regulated by dams up stream, otherwise the city would suffer from shortages during
summer time. For the year 2006 total water withdrawal for Zaragoza was 64.1 million
m 3 without including ground water (see figure 3).
600
500
Discharge (m 3 s -1 )
400
300
200
100
0
oct nov dec jan feb mar apr may jun jul aug sep
Months
Figure 3. Ebro river discharge at “Canal Imperial” diversion (Source: CHE, 2007)
Raw water quality in Zaragoza is very much affected by the seasonal fluctuations of
the Ebro River. Conductivity and hardness increase in summer time due to the strong
reduction in water discharge, making water eventually unsuitable for drinking
purposes. During spring and fall high discharges reduce conductivity but suspended
solids and organic matter –mostly humic substances exerting high chlorine
demands– significantly increase. More suitable water quality is achieved only during
winter time. High chlorine demands eventually lead to hyper-chlorination and to high
concentrations of oxidation and disinfection by-products. Several parameters of tap
water quality often exceed standard regulations (Local Agenda 21 Office of
Zaragoza, 2002). Due to these characteristics of raw water quality, drinking water
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