China's 'sponge cities' aim to re-use 70% of rainwater
http://edition.cnn.com/2017/09/17/asia/china-sponge-cities/index.html
In developing countries, rainwater often mixes with sewage. For example, in Philippines, I've seen slum area was sinking in flooding.
It's important to launch a system to purify appropriate amount of rainwater and to ensure the huge space to store them as appropriate status.
To supplement the function of Sānxiá Dam, which provide water for Shanghai, it's better to use rainwater.
