Potable water

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Potable water

By HERALDO CAMPOS*

Notes on the water quality of the Guarani aquifer

Source:

“The water that circulates on planet Earth, whether surface or underground, is part of the so-called Hydrological Cycle that began at the beginning of the cooling of magma and the consolidation of rocks in the Earth's crust more than 3,5 billion years ago. The escape of these gases and the capture of comets (full of gases and frozen water) by the Earth's orbit gave the beginning of this cycle and water resources, now known to be finite. The amount of water circulating is the same. We human beings interfere in its quality, polluting rivers and underground springs.

Most of the water that supplies underground reservoirs comes from rainwater. If we have a geologically prolonged dry season, the reservoirs will not be fed. The Guarani Aquifer, one of the largest groundwater reservoirs in the world, has plenty of drinking water. Calculations for global dimensions indicate that its reserves, in a volume stored around 7,5 million Maracanã stadiums, would be sufficient to supply the world's population for 10 years. However, we need to be careful with these numbers so as not to take them as a kind of “savior of the homeland”, or rather, of humanity.

The reservoir has a lot of water and is enough for everyone. It is a question of management and, if there is a difference in technological capacity among the four countries where it occurs (Argentina, Brazil, Paraguay and Uruguay), this difference has been minimized, due to the exchange of experiences between the technicians and the users involved. throughout the ongoing joint management process”.[1]

The path of water in the earth's crust is quite complex. Because of solar energy, a water molecule, by an infinitely large number of stimuli, can be evaporated from the ocean and return to it precipitated by the rains. It can also fall on the continents, infiltrating the ground below, be absorbed by plants or return indirectly to the seas through rivers and streams.

Where the water passes, it produces changes. It can dissolve minerals in rocks and drag their components far away for deposition. It can form rivers, lakes and oceans accumulating a considerable volume of aquatic species. It can overflow in flood areas and cause economic damage in urban areas. It can accumulate underground and form aquifers or groundwater reservoirs. […].

“The recharge water of underground reservoirs comes from precipitation or from surface water bodies, or even from other aquifers with which they maintain a hydraulic connection. Thus, the contribution of salts to aquifers depends, initially, on the chemical composition of the recharge waters and, subsequently, on the chemical interaction between these waters and the aquiferous environment. Therefore, its chemical evolution is directly influenced by the rocks it passes through”.[2]

In this way, the chemical evolution of this underground reservoir can be studied through its hydrogeochemical cartography, based on the existing physical-chemical analyzes in the study area, which, as a pilot, could be the coverage area of ​​the Guarani Aquifer in the state of São Paulo and then extending to all its occurrence in the Paraná Basin, in Brazilian territory, if the mass of data presents a good distribution density.

At the end of the proposed study, the integration of these mapped data, associated with the standards and parameters adopted in the analysis, can be visualized through a map of the chemical quality of the waters of the Guarani Aquifer for the different uses. In this final map the following cartographic elements would be represented: (a) main cities, (b) simplified outline of aquifers, (c) delimitation of classes in relation to uses and (d) local indication of pollution.

“The standards and parameters that serve as a basis for establishing the potability of water for human consumption and its suitability for irrigation and industrial purposes vary from one country to another. These patterns often seem to be more influenced by the chemical characteristics of the available water than by the effect on man's organic system or by the type of cultivation or industry in a given region. However, abundance or scarcity is the first factor that conditions its use. Thus, water of mediocre quality, but abundant, can become
more desired than good quality water, but in insufficient quantity.

The chemical concentration limits set or suggested by government agencies generally represent an adjustment between the desired quality, the available quality and sufficient quantities to meet demands. In this way, the adequacy standards for the different purposes contain a certain flexibility, since not all components have the same importance”.[2]

Thus, this study allows, through a review of the literature on this specific topic, to present a map of the chemical quality of groundwater for the different uses of this reservoir, which must be fraternally shared among the peoples who inhabit its region of occurrence. An example of this cartography was made for the region of Ribeirão Preto, located in the northeast of the State of São Paulo, whose largest city in this region, Ribeirão Preto, is supplied with 100% of the water from the aquifer to supply the different uses.[3]

“That's why I believe / Every night in the day, / and when I'm thirsty I believe in water, / because I believe in man. / I think we are going up / the last step. / From there we will see /
the truth shared, / Simplicity implanted in the earth, / Bread and wine for all.” (Pablo Neruda).

* Heraldo Campos, a geologist, is a postdoctoral fellow at the Department of Hydraulics and Sanitation at the School of Engineering of São Carlos-USP.

 

Notes


[1] Campos, HCNS & Canesin, MBS 2008. Guarani Aquifer: a 3×4 portrait of management and the experience with students in Ribeirão Preto (SP). Didactic Terrae, 3(1):74-85.

[2] Campos, HCNS 2013. Methodology for groundwater quality studies and its application for the hydrogeochemical characterization of the Guarani Aquifer. Didactic Terrae, 9(2):114-131.http://www.ige.unicamp.br/terraedidatica/>

[3] Campos, HCNS, Guanabara, RC, Wendland, E. 2010. Hydrogeochemical Map of the Guarani Aquifer – Ribeirão Preto Region (SP): Preliminary Results. In: Proceedings of the XVI Brazilian Congress on Groundwater. Saint Louis.

 

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