What is the difference between the water quality of Beijing South City and North City?

There is a considerable difference between the water quality of Beijing South City and North City, first of all, the water in the South City contains more alkali than the North City, but also because it is difficult to become, a long time ago, people live in, these live in the people's use of the groundwater is also more, and the North City, the contact time to be later than the South City, the exploitation and use of groundwater is not as serious as the South City.