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Water is of vital and critical importance to ecosystems and human societies. The effects of human activities on land and water are now large and extensive. These reflect physical changes to the environment. Global change such as urbanization, population growth, socioeconomic change, evolving energy needs, and climate change have put unprecedented pressure on water resources systems. It is argued that achieving water security throughout the world is the key to sustainable development. Studies on holistic view with persistently changing dimensions is in its infancy. This study focuses on narrative review work for giving a comprehensive insight on the concept of water security, its evolution with recent environmental changes (e.g., urbanization, socioeconomic, etc.) and various implications. Finally, it presents different sustainable solutions to achieve water security. Broadly, water security evolves from ensuring reliable access of enough safe water for every person (at an affordable price where market mechanisms are involved) to lead a healthy and productive life, including that of future generations. The constraints on water availability and water quality threaten secured access to water resources for different uses. Despite recent progress in developing new strategies, practices and technologies for water resource management, their dissemination and implementation has been limited. A comprehensive sustainable approach to address water security challenges requires connecting social, economic, and environmental systems at multiple scales. This paper captures the persistently changing dimensions and new paradigms of water security providing a holistic view including a wide range of sustainable solutions to address the water challenges.

a b s t r a c tWater pollution remains a challenging issue for the sustainable development of Kathmandu Valley despite several infrastructural, awareness-raising and policy measures. The paper assesses the sustainability of the surface water resources of Kathmandu valley by analyzing the water quality parameters such as Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD). The case study of Bagmati River pollution is analyzed for current and future wastewater production and treatment scenario based on the two important indicators of aquatic health. The DO and BOD were simulated to assess river pollution along a 25 km stretch between Sundarijal and Chovar. Water Evaluation And Planning (WEAP) model was used to simulate the current (year 2014) and future (year 2020 and 2030) river water quality conditions. The results showed that the water quality of the Bagmati River is relatively better during monsoon season due to higher river flow in comparison to the dry season. A comparison of simulated DO and BOD values for 2020 and 2030 with 2014 values indicated that the water quality of the Bagmati River within Kathmandu Valley will not significantly improve as a result of the planned wastewater treatment plants requiring additional countermeasures. The study pointed out the inefficiencies of the current practice of discharging untreated sewage into the surface water and causing largely in the river water and unsuitability of river water of water from the Gaurighat to the Chovar area. It is recommended to integrate river water pollution management and maintain ecologically to achieve the healthy urban development.

High fluoride (F −) groundwater causes fluorosis which might at severe stages lead to deformation of bones, bilateral lameness. The concentration of F − ranged from 0.4 to 4.8 mg/L. This study suggests that high HCO 3 − and Na + in alkaline medium along with water-rock interaction plays important role in enrichment of F − in groundwater. Na-HCO 3 is the dominant water type followed by Ca-HCO 3 suggesting dominance of Na + , Ca 2+ and HCO 3 − ions in groundwater. Factor analysis of water quality parameters suggests that four principal components account for 74.66% of total variance in the dataset. Factor 1 shows higher positive loading for pH, HCO 3 − negative loading for F − , Ca 2+ , SO 4 2− depicting ion-exchange and HCO 3 dominant water type responsible for F enrichment in groundwater. Saturation index for selected minerals suggests that most of the samples are oversaturated with calcite and undersaturated with fluorite. Calcite precipitation leads to the removal of Ca 2+ from solution thus allowing more fluorite to dissolve. These released Ca 2+ ions combine with CO 3 2− ions to further enhance the precipitation of CaCO 3 .

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