Addressing urban water scarcity: reduce, treat and reuse – the third generation of management to avoid local resources boundaries

Urban growth leads to geographically concentrated demand for water and food – and to growing volumes of wastewater and organic waste. Left unattended by city authorities, both local and planetary resources boundaries for water and nutrients will be transgressed. A novel partly dynamic ‘flexible water balance’ is developed to explore ways to address a looming water crisis. A systems-based flow chart shows how rainwater, groundwater and recycled water interact. Measures from supply-, demand-, and reuse management are combined to manipulate the water flows. Water management in Bangalore, India, focused on supply management over the period 1964 to 2015, tapping distant rivers. This mind-set was challenged by a Water Disputes Tribunal and international financiers. Residents and industry were losing faith in the erratic water supply, and met part or all their water needs by digging or drilling wells. The ‘flexible water balance’ is tested on Bangalore for the year 2050 when the population has increased from 8 to 20 million. New housing complexes can provide opportunities for effective arrangements to recycle water and nutrients, save energy, and reduce water pollution and air emissions. The ‘flexible water balance’ indicates that Bangaloreans can get enough household water without tapping river water and still recharge groundwater.