Sustainable water and energy supply have become two of the greatest global challenges of our time due to the fast-growing population and the depletion of fossil fuels.^1,2  Industrialization, water contamination, and climate change further plagues the problems of water scarcity. It is reported that over one-third of the current world population live in water-stressed areas, among which 1.2 billion people lack access to safe drinking water and 2.6 billion have inadequate sanitation.^3–5  The number of people that may be affected by water issues is projected to rise to over 3.5 billion by 2025. Though improved water conservation, maintenance...