Without proper water treatment healthy life in out cities wouldn’t be possible. To further couple the importance of water treatment to other sectors in the society we need some background information. This is described at http://en.m.wikipedia.org/wiki/Water_treatment

Also, how drinking water is made and how water treatment plants function is explained in:

With this background information and with the expected prognoses that 70% of world population will be gradually moving to cities during the twenty first century it is not clear how water treatment plant would cope with the increasing waste that is generated from human consumption, i.e. household, agriculture and industry. Unlike solid waste, which is subject to sorting in some parts of the world, wasted water from urbanized areas carry an increasing number and amounts of pollutants in their end products, i.e. effluents and sludge. Though water treatment plants may be effective to provide good quality of water, wastewater treatment plants however are not as effective in removing whatever exist in wastewater. This means that the net effect of urbanization is an increasing production and injection of waste and pollution that is delivered to natural aquatic water systems. This would, of course, provide large-scale and long-term threats on ecological water, and life quality, and will have negative feedback effects on “raw” water that will be later used in water treatment plants.

In summary we have an accelerating internal urbanization of water that generates waste and pollution as end products to be injected and delivered to the main natural global water cycle.