group of systems are estimated to increase availability to 73 m<sup>3</sup> /s in 2010<sup>6</sup> . At this time, urban demand is estimated at between 69.8 and 78.6 m<sup>3</sup> /s. Other solutions will be needed in the middle to long run, such as water demand management, reuse, and expanding existing system capacity, or constructing new systems, most likely through importing water from adjacent basins.

**Uncontrolled use of groundwater resources.** Although the users in the Alto-Tietê basin are almost exclusively supplied by surface water, aquifers are an important supply alternative under scarcity conditions. Recently, a significant and worrisome increase in groundwater abstraction has been observed. A 2000 study estimated groundwater extraction in the basin at 7.9 m3/s, and expected it to increase to 10.9 m3/s by 2004, and to 16.5 m3/s by 2010. Industries are the largest consumer group in terms of number of wells (35%), followed by private homes and apartment buildings (25%) and services (24%) (FUSP, 2002b).

This increase is partly a result of SABESP’s price policy and partly because of the lack of monitoring and control of groundwater use (FUSP, 2002b). In the municipalities not served by SABESP, where water and sanitation is provided by local government, groundwater extraction has also increased substantially. According to interviewees, this can be attributed to municipal governments’ general lack of capacity in managing and expanding urban services. In general, the exploitation of groundwater resources has been systematically precarious and uncontrolled. The consequence is the lowering of the water table and a resulting increase in pumping costs, as well as the possibility of well contamination, potentially expanding to the most protected zones of the aquifer (Hirata _et al_ , 2002)<sup>7</sup> .

**Water resources protection and urban expansion.** Water supply for various uses is highly dependent on the Alto Tietê’s public water supply systems, mostly operated by the state water sanitation company (SABESP- _Companhia de Água e Esgoto do Estado de São Paulo_ ). However, population growth in the metropolitan area is moving precisely towards the main sources of drinking water. The causes are related to the lack of housing policy and high income concentration, both of which have fostered the growth of an informal housing market. This informal market is difficult to regulate through the command-and-control land use policies currently in place. Ultimately, areas that are more tightly regulated (but where enforcement only involves the emission of licenses and permits necessary to carry out a formal activity) are most subject to the expansion of informal land uses, since formal activities are not permitted in those areas.

Figure 3 shows the location of the three most important water source systems (Cantareira, Guarapiranga-Billings, and Alto-Tietê) as well as the urbanized area of the region, showing how the city is advancing into water source protection areas.

> 6 The Alto-Tietê Basin Plan indicated that the planned infrastructure projects for the basin would increase availability to 66.2 m3/s in 2004 (FUSP, 2002a).

> 7

> The problems related to the exploitation of groundwater resources in the Alto-Tietê basin are extensively analyzed in Hirata, Ferrari, Ferreira _et al._ (2002).

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