The city's underground waterways

Rainwater finds different paths to return to nature. It does this without filters, after sliding on all kinds of surfaces and carrying with it the contaminants of the place. Solutions to reduce rainwater pollution are being researched in some European cities. In Donostia-San Sebastián, for example, filtration systems have been installed at the outlets of rainwater in different neighborhoods to retain suspended solid pollutants by decantation.