How many people are there in the world?

7.7 billion

The world's population reached 7.7 billion in mid- 2019, having added one billion people since 2007 and two billion since 1994. The growth rate of the world's population peaked in 1965-1970, when it was increasing by 2.1 per cent per year, on average.

Explanation:

There is over a billion people on Earth

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.