The water travel forms the basin

It rained. Accumulated rain water that permeated the dense forest soil forms an underground water reserve, that finds a way through and springs from the ground. Runs on the Earth surface according to the gravity law. Goes away, searching for its path. Reaches another stream further. They merge and give birth to a brook, a higher volume water unity, that flows more intensily.

Away from there, but in  the same region, it’s from a gap in the rock that the rain water arises to the surface and starts to run and follow its course to meet the other streams on their way.

Popping up here and there, springs become ponds, streams, flowing waters that come either from the dense and humid forest soil or from the cracks onto rocky ground. Slowly, they begin to meet each other, to add and form streams, brooks and rivers by diverses paths, compounding an entanglement of water courses. This complex net of water courses that is growing meet the largest river that, at the end, in most cases, merges its waters into the ocean, or into another major river thar finish in the ocean.

These water paths entanglement and all the region bathed by it is what receives the name of hydrologic basin. On Earth there are some basins that end up into lakes. There are also su-basins that are smaller, but not less important to life. 

São Paulo State gathers some very large basins, territorialy speaking, such as the Tietê River basin. From its spring to the delta it runs 1,100 km, from East to West within the State. A system was created to work at the hydrologic management per basin within the State, that divides the territory in 22 hydraulic resources management unities, accordingly to the physical limits of each basin or sub-basin. 

Water status in the State is considered good. Water availibility per inhabitant/year is 2.9 thousand cubic meters. Although the distribution of this water is not proportional and in four regions the water shortage already reaches levels considered critical:

1.       Tietê Region – with 200 cubic meters inhabitant/year – 1/7 th from minimum rate

2.       Piracicaba Region – 400 cubic meters inhabitant/year

3.       Turvo Grande Region – 900 cubic meters inhabitant/year

4.       Mogi Region – 1,500  cubic meters inhabitant/year

Alto Tietê basin, with only 400 cubic meters inhabitant/year is the most populous and with the major social and economic gaps. It is formed by the São Paulo metropolitan region, that would need 400% - that is four times more water than it has – to meet the demand of its population at proper levels.

To fight shortage and supply 17 million people, it was necessary to reach for water in another basin. Through the Cantareira system, takes clean water from the Atibaia and Jaguari Rivers – located at the Piracicaba/Capivari and Jundiaí – and throws back this water, totally polluted – to the interior, in Tietê and Pinheiros Rivers, which negativelly impacts the life quality of people that live on the borders of rivers from other hydrologic basins. This generates serious social, economic and environmental issues and one of the major conflicts for water within the State.