What might happen to the salinity of the ocean if animals were no longer living in it?

The salinity of the ocean and oceanic animals are not related. Living organisms are not the cause of the salt in the ocean, so if they no longer lived there would be no change.

what's the question?

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.