The planet’s freshwater resources, if managed sustainably and effectively, can meet water demands of the world’s growing population with good quality water. However, water scarcity and water quality degradation present major challenges in securing enough water of good quality to meet human, environmental, social and economic needs to support sustainable development of countries. The widespread water quality degradation across the world is the most serious water problem, threatening human health and ecosystems’ integrity, but also representing a major concern for the water resources sustainability. New water quality challenges such as emerging pollutants and safe wastewater reuse bring even greater concerns, calling for urgent attention.