Green, soil and water are powerful means of ecological design in public neighbourhood spaces. These spaces, which form the urban "porosity", become, in an eco-sustainable approach, multipurpose systems suited to improve the urban metabolism (oxygen production, recycling of water and organic wastes) through the use of space itself as shaped by soil movements, water pools and green masses. Open spaces at neighbourhood scale are increasingly crucial means of enhancement of environmental urban quality, which does not imply that historic towns have to be transformed in woods, nor in new garden city models. The quality of neighbourhood life could be improved by solving the problem of water saving by systematic recycling, so that trees and green masses can be allowed to grow up and mitigate the summer microclimate through evapotranspiration while bettering the air quality by oxygen production. Mitigation of summer microclimate means energy saving in artificial air conditioning and reduction of CO2 and heat from air conditioning plants. A proper design outcome could be obtained through a truly integrated approach and should produce both agreeable places to live in and self-sustaining and balanced ecosystems. The paper will deal with possible strategies for the use of green, soil and water as means of ecological design in public neighbourhood spaces, while testing the minimum surface dimension suitable to obtain substantial advantage degrees in water recycling, summer microclimate mitigation and air cleaning.