HANGZHOU - Hangzhou, the host city of this year's G20 summit, has launched a project to transform itself into a sponge, capable of soaking up rainwater and retaining it for future use.

According to the city government, new public buildings, residential communities and industrial parks will have to install green roofs or rooftop gardens to absorb rain, as well as cleaning and recycling facilities.

The existing sewer system will be upgraded. Wetlands, filtration pools and permeable public spaces will be added to store water for irrigation during dry seasons.

The project will turn at least 20 percent of the city "spongy" by 2020. Over 80 percent of the city will be able to meet the requirement of a sponge city by 2030.