We're destroying our source of survival. WATER POLLUTION.

As teachers have always told us since the very first years of school, water is essential for life. They taught us the water cycle, that it covers 71% of the earth's surface, that it makes up 65% of our bodies. 
Now, water is becoming increasingly polluted and this is a threat to our health, to the fertility of the soil and to the survival of wildlife. 

Water pollution is the result of human activities. 
The water we daily use in our houses and industries is taken from lakes, rivers and from the underground and, after we have used it (and contaminated it) most of it returns to these locations. 
If this waste water is not treated before it is discharged into waterways, then serious pollution will be the result. 

To prevent water pollution we should remove the pollutants before the water gets back into the environment. 
When the polluted water of the rivers arrive to the sea the nitrates and phosphates create beds of green algae and produce periodic catastrophic loss of marine life. 
In the 60s the Thames was biologically "dead"...nowadays the quality of its water is better. 

This situation is worse in the developing countries, where environmental policies are often almost non-existent and hazardous substances are used in the industrial processes and then poured out into lakes and rivers. 
Lots of people in these countries die because of the contaminated water and many ecosystems have been or are being destroyed. 

(Thanks to Lorenzo S. for helping me writing this post)