New companies are sprouting to meet this demand, and existing companies are expanding. In Britain, the growth has been especially explosive: Manufacturers say the use of rainwater harvesting systems has shot up 300 percent in two years, and the number of companies in the green roof business has increased fivefold as the surface area of roofs installed has nearly doubled.
The techniques themselves have been around for thousands of years - think Roman cisterns and the hanging gardens of Babylon. Their modern incarnations were pioneered by Germany in the 1970s, when existing sewage systems where unable to cope with heavy rains. Now green roofs and rainwater harvesting systems are omnipresent there and in Austria and Switzerland, with many local authorities requiring new buildings to include one or both. In Germany alone, industry data show about 14 million square meters, or 150 million square feet, of green roofs are installed annually, and 80,000 rainwater harvesting plants are built each year.
Most other countries are still far behind Germany, but in the past five years they have been catching up. "It's becoming more mainstream," said Chris Williams, the chairman of the UK Rainwater Harvesting Association and the chief operating officer of Hydro International, a water management and treatment company based in Britain. "Climate change is occurring, and both industry and governments are starting to respond and react."
Green roof at Mountain Equipment Coop in Toronto, via Flickr, Bruce Mau and Skeezix1000. Wikimedia Commons