BACKGROUND

It is very clear that for the world, water is a critical resource that will become increasingly scarce in the coming decades. Of the earth's freshwater, about two-thirds is polar ice and most of the remainder is groundwater of depths about 200 to 600 metres, but most groundwater is saline below this depth. Freshwater in rivers and lakes, as estimated by UNESCO (1978), is about 93,120 cubic kilometres (km3), about 0.266 per cent of total freshwater in the world. Compared to total water supplies in the world (freshwater and non-freshwater), rivers and lakes only constitute about 0.0072 per cent of the total. That is why water is now a very critical and important resource for human development.

In Southeast Asia, the average water availability per capita is about 4,900 cubic metres (m3), but the water resources vary with space and time. For example Laos has the highest water per capita (about 35,000 m3), while Singapore has the lowest (about 155 m3), with Vietnam (an inland country) estimated at about 3,870 m3. For most rivers in the region, water flows during the flood season occupies about 70 to 80 per cent of the total water supply during the year. For Southeast Asia, the Mekong River is the largest, with a total watershed area of 795,000 square kilometres (km2). The length of the main river is 4,400 kilometres (km), and average discharge is 15,000 cubic metres per second (m3/s). The Mekong River Basin flows across six countries: China (165,000 km2), Myanmar (24,000 km2), Thailand (184,000 km2), Laos (202,000 km2), Cambodia (155,000 km2), and Vietnam (65,000 km2).