Water pollution is the result of human activities as almost any human activity can have effect on water quality. Contamination of lakes, rivers, and oceans happens every day threatening animals and plants that live in these water bodies. Water pollution is burning problem that needs to be solved but this is very difficult because there are so many different causes of water pollution, and we should solve every single cause in order to completely solve this problem. However we can point out two main causes for water pollution: sewage waste and waste water.
When thinking about water pollution many people think primarily of sewage waste. This is understandable given constant increase of human population, and the fact that many people in undeveloped countries still lack even the basic sanitation (toilets). Sewage disposal problem is more serious problem than many people think, and it often results in water-related illnesses such as diarrhea, that by some estimations kills more than 4 million children each year. But the problem with sewage doesn't lie only in countries of the third world, but also in many developed countries. For example, when you flash the toilet, waste goes somewhere, sometimes even into the sea. Now if this would be completely "natural sewage" then this wouldn't be big problem because 90% of sewage is water. However we are definitely changing this percentage by flashing down paper, plastic, and many other wastes which eventually enter into our river bodies, and can cause many waterborne diseases.
Waste water is problem that has been there since the beginning of industrial era. Waste water are different chemicals discharged mainly by factories, of which much gets pumped untreated into rivers, oceans, and other water bodies. The world generates each year incredible number of 400 billion tons of industrial waste, of which many ends up in different water bodies. Factories are mostly responsible for waste water problem, but are not only factor. Another significant contributor is also a highway runoff, especially now with so many different vehicles on our highways. Spilled fuel, different brake fluids and similar stuff are all toxic chemicals. When it rains these toxic chemicals are being carried to rivers and other water bodies.
Sewage waste and waste water are problems that deserve our attention, not only because of many different ecosystems that have to live in polluted water bodies but also because of ourselves, especially because of freshwater supply in many parts of the world. Without the water there is no life on Earth, and we have less than 3 % of fresh water on earth, of which majority is frozen in glaciers.
Solving the water pollution problem is especially difficult task in undeveloped countries that lack both funds as well as the education to understand the importance of keeping the water sources clean. There are still some people dying of thirst in some countries, and this is really moral slap in the face for all of us, since water should be resource available for all of us, and not just for the lucky ones.