The many different urban arrangements of the present time have advantages and disadvantages in terms of dealing with water. The North American traditional suburb, for example, present a high degree of permeability and has in the large lawn its most valuable asset, but it is unsustainable from the point of view of transit and extremely harmful to the natural environment for occupying vast amount of space with very low densities.

Areas such as the Plano Piloto in Brasília seems to provide the best of both worlds: reasonable density, public transportation and high permeability. But the cost (those who live in Brasília know better) it is prohibitive for a large portion of the population.

 

On the other hand, the traditional city suffers from the opposite problem: high densities are necessary to cover the cost of the infrastructure and the concentration of services, making possible good transit solutions and consequently lower energy consumption. However, the use of space is so intense that almost nothing is free for water infiltration, causing heat islands due to absence of evaporation and flooding whenever it rains.

It is precisely in the traditional city that individual responsibility can make the difference.

Let’s see the numbers:

In a normal block of 1ha (10.000m2) 100 thousand liters of water fall every time it rains 10mm (almost daily during the summer). If the block entirely covered, that volume of water goes immediately down slope via storm-water system or over the streets.

Since each building can achieve zero discharge with a garden of 18x18ft or 800sqft of permeable pavement, the rate of infiltration can gradually return to pre-urbanization levels if each lot take responsibility for the corresponding volume.

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