Cities can make more efficient use of energy, water and other resources. More emphasis on sustainability can lower the urban ecological footprint considerably.
Traditionally, cities are big users of raw materials brought in from elsewhere. Hardly any thought has been given to 'urban harvesting', says Agudelo. But cities certainly have a lot to harvest, such as rain water or energy via solar cells or boilers, and also recycled waste flows. For example, slightly polluted water can be used for flushing toilets, and excess heat in a supermarket can be used to heat up swimming pools.
All in all, these measures can have spectacular results. A typical Dutch city, according to calculations by Environmental Technology, can provide its own electricity requirements and generally half the piped water it needs. 'This is just one of many examples. Our methodology works just as well in Manhatten as in Mexico City. We design simple tools with which city designers and architects can work with. An integrated planning process would bring about many benefits. One green roof or a few solar cells are not enough. There is a need to re-use waste flows as well.'
Although good results have been obtained in the study, it would take decades before such sustainable principles can be implemented on a large scale, thinks Agudelo. 'Although cities are constantly being renewed and districts are being renovated, such changes take time.' Co-author Rijnaarts adds: 'In the Netherlands, 100 billion euros have been invested in infrastructure for water supply and waste water handling. Such matters surely cannot happen overnight; they progress gradually. On the other hand, in new residential areas, or if a new city is to be built in China within several years, urban-harvesting principles can be applied immediately.'
In some houses and districts in the Netherlands, very promising results have already been achieved. However, the ideas from Wageningen are still not commonly accepted. 'The realization that things can be different has not sunk in yet. For the time being, the main task at hand would be to bring attention to good ideas and techniques, raise awareness and set up model projects,' predicts Rijnaarts. 'Many people still think that sustainability leads to inconvenient adjustments, but we can get many benefits without having to give up comfort.'