The freshwater available on the planet earth is enough that it can meet the demands of humans. But the distribution of water is not proper. For Example the Citizens of Bahrain, a tiny island in Persian Golf, have no freshwater availability and they desalinize the water for use. The per capita utilization of water vary from continent to continent and from one country to other country. Some countries receive the more water but their utilization is not proper while some have low water availability but they use it in effective way. South America and Asia together receives almost half the share of water resources of world. South America receives more water compared to Asia but South America has not the much potential to support the people with water. That's why the water falls in Amazon River that has poor soil and it does not support the agriculture. Asia receives less water than South America but water supply support the humans because the land where precipitation falls is suitable for agriculture.
Global water supply greatly depends on the stable runoff. For example, India has wet season from June to September. Although the precipitation is high but their utilization is low because the water quickly runoff to the rivers and water is not available during rest of months.
Drinking Water Problems
Many developing countries have lack of water supply for drinking purpose. According to WHO there are about 1.4 billion people that lack the access to safe drinking water supply. These estimates also represents that 2.9 billion people have not the access to dispose wastewater and fecal waste. According to WHO 80 % of human illness are caused by insufficient water supply, water poor quality and lack of sanitation facility. The US agency for International development assisted the areas that are subject to drought in the Sahel regions of Africa. Both United Nations and World Bank are dealing with water management projects.
Water Problems and Population Growth
Population growth is exceeding the water demands of countries. In India 20 % of population has the access to only 4 % of world's freshwater and 8000 villages have no local water for use. One third of wells in Beijing have been dried. The main aquifer that is supplying water to Mexico is dropping at the rate of 3.5 m per year. Global water shortage also leads to shortage of food supply.
Water Resource Sharing among Countries
Water is often an international resource. About three fourth of world's 200 watersheds are shared between atleast 2 countries. Management of rivers are are on cross boundaries needs international cooperation between countries.