Drinking water treatment in developing countries to eliminate chemical, physical and biological pollutants can be carried out by various methods. Moreover, conserving water by Rain Water Harvesting and waste water reuse after appropriate treatment is also the need of the hour owing to the huge water demand globally. To address each of these important topics, six case studies have been discussed in this chapter. The first case study highlights a technology that can reduce arsenic in drinking water while the second one emphasizes the use of natural techniques such as herbs for drinking water treatment. Conservation of rain water by collecting it on rooftops is described in the third case study, and waste water reuse for non-potable and indirect potable purposes is accentuated in the fourth case study. The fifth case study explores lake water treatment in developing countries and finally in the sixth case study, the use of hydrodynamic cavitation in hand pumps for disinfection of bore well water is elaborated. Each case study explores the said possibilities for a developing nation, particularly stressing the economic and technical feasibility in such locations.