What do water filters have in common with CO2 emissions certificates? More than you might think. This week on Global Ideas, reporter Grit Hofmann takes us to Kenya, where a European company is handing out life-saving filters that decontaminate water. What’s more, the devices are free. In return, the company receives emissions certificates that can be sold on the carbon trade market. It’s a win-win situation for everyone involved, from the company to the customers and the environment, too. Our in-depth text takes a look at Hamburg-based "Viva con Agua," an initiative for clean drinking water across the world. Author Po Keung Cheung speaks to founder and former footballer Benjamin Adrion.