Natural fresh water, does it exist? We used to have high quality natural waters but this was probably more than a couple of thousand of years ago, i.e. just before the Roman Empire. Natural fresh waters are very hard to find nowadays, only in remote regions far away from human impacts, e.g. frozen water in polar areas or some fossil water somewhere underground.
The Romans invented the culture of urban water systems that exist today in our cities around the world. Gravity-fed systems distribute water, from water treatment plants, around cities and ultimately dispose wastewater in underground sewer networks. From the Romans time until today urban water systems went through major transformation forced difficulties originated from: water shortages during the Romans; cholera outbreaks in the Industrial Revolution; and most recently polluted surface water systems (lakes, rivers, …… ), e.g. in Europe and the US that accelerated shortly after WWII. We are now facing more and more complex web of serious threats on natural waters due to the rapid technological and economical advances of the past century, the growing world population and an accelerating “production-consumption” wheel as a result of many emerging economies. Climate change, pile-up of pollution and waste, aging urban water systems (both water and wastewater), various types of peaks in particular energy- and water-related ones, constrains in world economy and geo-political conflicts. You name it.
In this post “Sustain-earth.com” gives some background information of the evolution of urbanized waters and problems associated with wastewater treatment. In coming posts other urbanization-related issues will be given, in particular water treatment processes and the importance of the quality of natural waters on such processes.
Here is some description of how urbane water systems developed and the situation many cities are facing today. Urban water systems are starting to break down with these problems: 1) water infrastructure needs costly upgrades; 2) many sewer systems are becoming overloaded; 3) water scarcity appearing in drought-prone areas. Some possible fixes are, also, given: Water recycling, desalination, decentralization: http://www.vox.com/2014/10/6/6900959/water-systems-pollution-drinking-water-desalination
Wastewater Treatment Plants have impacts on the water quality of natural waters and there are growing fears that they are acting as pollution factories: http://www.riles.org/musings.htm
Also additional background information on how typical wastewater treatment plants work: http://water.usgs.gov/edu/wwvisit.html see also this video: https://www.youtube.com/watch?v=OocKzAowo_0&app=desktop