Bauru is an ideal laboratory for comprehending and suggesting solutions for water security.

The study area

The study area Situated in the upper portions of the Batalha and Bauru river basins, it comprises parts of the municipalities of Bauru, Piratininga, and Agudos. This region is located in the center of the State of São Paulo, within the Tietê-Batalha and Tietê-Jacaré Water Resources Management Units. The main urban center and focus of the research is Bauru, a prominent regional economic hub, with a population of 380,000 inhabitants, and a GDP of R$ 15 billion. Another center is Piratininga, with a population of 12,000 inhabitants and a GDP of R$ 260 million.

The region's water problem

Despite Bauru's public water supply coming from a capture in the Batalha River (13.2 Mm³/year) and 39 deep tubular wells in the Guarani Aquifer System (34.6 Mm³/year) (2021 data), the city is one of the most vulnerable to droughts in the state of São Paulo, with a history of successive water crises. This issue has led to the drilling of over 400 private tubular wells in the Bauru Aquifer System, extracting 2.34 Mm³/year, totaling a water production of 50.14 Mm³/year for this city. This flow, even if sufficient to meet all its demand, is not due to some factors: 50% of the distributed water is lost due to leaks in the network and at the water treatment plant; there are limitations in the operation of the non-interconnected network; the Batalha capture is in a small basin, with high competition for water (rural use) and serious problems in its reservoir; and there are regions where the Guarani Aquifer System has low production. Thus, the reasons explaining the water crises go beyond a simple failure in the water sources' supply.

Issues with the sustainability of the water supply

In the Guarani Aquifer System: Groundwater recharge is very slow (over 100,000 years), classifying them as fossil waters. Therefore, the continuous and unplanned extraction of these waters could lead to the depletion of the aquifer, resulting in a constant increase in costs for its extraction.

In the Bauru Aquifer System, which occurs beneath the city and presents an extensive contaminant plume consisting of nitrate and other compounds up to 60 meters deep, generated by the leakage of the sewage network, restricting the use of groundwater and putting private users at risk.

Important issues identified in the region.

Water quantity

•Decrease in water withdrawals from the Batalha River during droughts;

•High level of water losses in the water supply system of Bauru;

•Areas in Bauru affected by supply failures (rotational cuts and requests for water truck deliveries);

•Increase in withdrawals from the Guarani Aquifer System (non-renewable water, recharge takes over 30,000 years).

Water quality

•The Aquifer System Bauru contamination by nitrate, heavy metals, hydrocarbons, and chlorinated solvents, due to leaks in the sewage network and other polluting sources;

•Discharge of raw domestic sewage into rivers in the urban area of Bauru;

•Siltation and eutrophication in the upper part of the Batalha River.

Management and other matters

•Lack of compliance in the drilling of private wells: a significant number are operating without authorization, despite being registered with the DAE;

•Development of condominiums in subdivisions within the APA of Rio Batalha region.

The solutions of SACRE

The municipality of Bauru offers "other waters" still little explored for public and private supply, which are those that SACRE is studying to be incorporated into the public and private system. In the range of alternatives are:

• Systems using the river-aquifer binomial;

• Managed aquifer recharge;

• Treatment of polluted groundwater with nature-based and engineering solutions; and

• Instruments to improve water resource management and governance, with water resource allocation processes.

Solutions not only for Bauru

Many of the problems in Bauru are also found in other Brazilian cities, allowing the solutions developed by the project to be transferred and adapted to these locations. New science-based solutions are being considered as public policies, bringing technologies closer to society in a very organic way. SACRE also evaluates trade-offs, based on a deep understanding of various ecosystems and social and economic interests, to bring the most benefits to the environment and society, especially in scenarios of limited water resources and pressured by global climate change.