They have been doing it for centuries in parts of Africa and Asia, and in more recent times in Japan and Germany. Urban rainwater harvesting - capturing rainwater on rooftops into storage containers is one of the simplest and oldest methods of capturing water.
With climate change predicted to increase the intensity and variability in rainfall, urban rainwater harvesting is catching on in cities in Europe. Sweden, however, is lagging behind, according to Bo Olofsson, a professor in environment geology working at KTH, (the Royal Institute of Technology in Stockholm).
He tells Radio Sweden that it is time to save water using the old, traditional methods.
"We are not used to rainwater harvesting. It is new in Sweden. We should look at the water not as a problem, either we have too much with flooding or not enough.We should look it as a fantatsic value that can be used and harvested."
The collection of rainwater from rooftop catchments is being promoted as a technical solution for supplementing household and commercial water supply. In developing countries, rainwater harvesting is used to collect water to drink (potable), while in developed nations, it is typically collected for toilet flushing and watering the garden or washing clothes.
Professor Bo Olofsson says in Sweden, water is wasted , with huge losses due to evaporation and run-off before it becomes polluted. He says that urban rainwater harvesting will save water and reduce the burden on treatment plants that cannot cope with large, short bursts of water.
"We have plenty of problems because we can't cope with these extreme situations that we will in the future with very heavy rain. Our pipes are not built for that, so we have flooding onto the streets where it gets polluted. Treatment plants cannot cope with a great amount of water at the same time," he says.
Ground-surface rainwater harvesting is another method which diverts water flowing along the ground into a tank below the surface.
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