Cities can make more efficient use of energy, water and other resources. Cities are like 'The Very Hungry Caterpillar', swallowing up resources and dumping their waste outside their boundaries as fast as they can. A pity, as attending to sustainability can significantly reduce a city's ecological footprint.
Traditionally, cities are big users of resources 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 from 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 Manhattan 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. You won't get there with one green roof or a few solar panels, though. You need to re-use waste flows as well.'
Changes take time
In spite of the study's promising results, it will take decades before such sustainable principles are implemented on a large scale, thinks Agudelo. 'Although cities are constantly reinventing themselves and neighbourhoods get renovated, such changes take time.' Co-author Rijnaarts adds: '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. 'For the time being, the main thing is to propose good ideas and techniques,' says Rijnaarts. 'Many people still think that sustainability leads to inconvenience, but we can get many benefits without having to sacrifice any comfort.'