The Thai government is working seriously at maintaining Thailand's water at international standards, and in its second Stimulus Package (SPII), committed to invest in the water-grid system an amount valued at 230,645 million baht accounting for 14.7 percent of the total package value.

The combination of industrial growth, population growth and rising incomes has led to an increased demand for water. Demand is estimated to be growing 20 percent a year, but the investment program of the Provincial Waterworks Authority (PWA) has increased supplies about 12 percent a year. The PWA has the capacity to serve about 60 percent of the 10 million people living in the 220 cities and towns under its jurisdiction with about 1.2 million cubic meters a day.

Demand for water is about 53 billion cubic meters annually. Out of the volume, almost 90 percent is allocated for agriculture, 6 percent for consumption, and the rest for industrial use. Demand for water in the country is estimated at 70 billion cubic meters annually in the next 10 years. Thailand consists of 25 river basins, with an annual rainfall between 1,200 and 2,700 millimeters. The amount of average annual runoff is 200 billion cubic meters, but only 38 million cubic meters, or 19 percent, can be stored in reservoirs.

The Chao Phraya Basin

The Chao Phraya basin is the most important basin in Thailand. The Basin covers 30% of Thailand's land area, is home to 40% of the country's population, employs 78% of its work force, and generates 66% of its Gross Domestic Product (GDP).

The total population of the Chao Phraya basin was 23.0 million inhabitants in 1996. The Basin can be divided into eight sub-basins based on the natural distribution of its river system. About 50% of this population (11.5 million) resides in the Lower Chao Phraya basin, in which the highly populated areas of Bangkok Metropolitan Area (BMA) and its environs of Samut Prakan, Nonthaburi and Pathum Thani are located.

Similarly there is a large concentration of population in the Upper Ping where Chiang Mai (the second largest city in Thailand) is located. Overall, about 68% of the total population of the Basin is rural, but there is considerable variation with over 90% of the population being rural in the Upper Chao Phraya basin compared to 45% in the Lower Chao Phraya basin,

It is projected in the next decade that the rural population will decrease by an annual rate of about 1.31% and that the population growth rate will remain low at about 1.0% per annum. These trends should ultimately induce aggregation of farming land with consequential increase in household incomes. Population density averages 136 persons/km², but varies greatly from 44/km²in the Nan Sub-basin to 533/km² in the Chao Phraya Sub-basin. Bangkok and its vicinity have the highest population density of 1,497 inhabitants/km².

Dams

Over the years the government has constructed some 3,000 dams to store the monsoon flows for release in the dry-season to exploit the Chao Phraya basin's vast agricultural potential and to meet the growing demands of industrial and urban users.

The two largest dams constructed were the Bhumibol and Sirikit Dams to supply stored water for electricity generation, irrigation, and domestic and industrial water use. Together these two dams control the runoff from 22% of the area of the entire basin. Bhumibol Dam on the Ping River has a live storage capacity of 9.7 billion cubic meters (bm³), compared to the average annual inflow of 6.6 bm³ from a drainage basin of 26,400 km². The installed hydroelectricity generation capacity is 713 MW. The dam was completed in 1963, and filled for the first time in 1970. Sirikit Dam on the Nan River was completed in 1972 and has a live storage capacity of 6.0 bm³ compared to the average annual inflow of 5.9 bm³. The installed hydroelectricity generation capacity is 500 MW.

Several other large dams (Kiew Lom, Mae Ngat, Mae Kuang, Mae Chang, Thap Salao and Kra Sieo) have also been built during the last 20 years to increase the total surface water storage in the Basin, and recently another dam, the Pasak Dam, was commissioned in 2000.

Domestic Water Use

Water supplies for domestic purposes are provided by water service facilities in urban areas and by wells in rural areas.

At the provincial level, domestic water supply coverage is about 47% of all households. Water supply for domestic purposes for farm households is from piped schemes (56.8%) ,wells (37.2%) and rivers (6.4%). Overall, 62% of rural households consume water from unprotected sources, such as rainfall collection, rivers, canals and ponds. The majority of piped schemes for farm households are operated and managed by village communities.

Nationwide, potable water supplies are generally provided by two agencies: the Metropolitan Waterworks Authority (MWA) and the Provincial Waterworks Authority (PWA). The MWA engages in production and distribution of potable water in the Bangkok metropolitan region while the PWA is responsible for all the provinces in Thailand. The PWA is responsible for water source development, conveyance, pumping, treatment, storage, and distribution facilities from all urban and rural communities in the provinces.

Source: Natural Water Resources Committee (ONWRC) of Thailand

Updated 11 June 2010