The Then Poignant River Thames and The Ganges River of Today
It is not only the Ganges river only, there are few blue rivers, nowadays anymore worldwide, except on the hinterlands beyond cities, where rivers are sourced and originated from glaciers or the like, as shown on the Water Cycle Diagram ( http://texaslivingwaters.org/wp-content/uploads/2013/03/USGS-water-cycle.jpg .)
It is a catastrophe too that the city-water coming to your premises are taken from such non-blue / black / dead rivers; in many occasions, however, getting treated in the treatment pants. But there is a big concern, if all water treatment plants worked efficiently worldwide, and if they could get rid of all sorts of known and unknown harmful compounds, widely spread all over, otherwise most people wouldn't opt for the additional treating, via small packaged units; retreating the city water.
The widespread pollution on the environment might eventually convince humans opting for the treated rainwater harvested, as potable water; as being practiced by www.chooserain.com; it is off the city-water grid, for a long; even providing the well-treated harvested rainwater, in biodegradable bottles. That is quite a wise option, in the world of widely spread pollutants, ending up in water streams anyawy:
Compare Two Journeys of the Raindrops; Then Judge on the Humans Negligence on the Water Management, in the Course of History!