Water pollution could be traced to the outlet. There are deliberate dumpings by factories. Manure that is used for the agriculture is harmful for the groundwater. An oil tanker that loses oil is also a polluter. Water pollution without outlet is acid rain and gases that are released by the industry and transport. They penetrate the earth and run to the groundwater. Acid rain (or more accurately acid precipitation) occurs when sulphur dioxide and nitrogen oxides are emitted into the atmosphere, undergoing chemical transformations and are absorbed by water droplets in clouds. The droplets then fall to earth as rain, snow, or sleet. This can increase the acidity of the soil, and affect the chemical balance of lakes and streams. The emission of sulphur dioxide(SO2), nitrogen oxides (Nox) and ammonia (NH3) form in the air acids (the nitric acid and the sulphuric acid), which through wet precipitate (such as rain, snow and hailstone), dry precipitate (such as gasses) or trough fog come down. You also could be polluting the water, by using some sorts of cleaning products and pesticides, and flushing paint of bleaches.
