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Environment and health
In 2004, surface water quality classified as ‘good’, ‘fair’ and ‘poor’ accounted for 48 percent, 32 percent and 20 percent respectively. The classification carried out by analysing the quality of samples of water taken from natural waterways throughout the country. The overall situation has improved compared to 2003. Critical areas are: lower Chao Phraya in central Thailand and Lower Lam Takong in northeast Thailand. In the North, Northeast and South water quality is good (surface water quality) and improving, while the Central is good with mixed improvement, and the East is fair and stable.
In 1999, in the northeast, 10 percent of the irrigated land was affected by salt. The presence of the salt bearing nature of the soil parent material has been identified as the primary cause. Other activities, such as irrigation, could be classed as secondary causes for accelerating this condition locally. Many programmes have been launched to correctly manage cash crops and paddy on saline soils. Salinization is now reported to be affecting large areas in the coastal parts of the central plain.
Bangkok faces problems of both too much and too little water. Flooding occurs frequently in the wet season owing to low average elevation, high tides and inadequate drainage. The Metropolitan Waterworks Authority is unable to supply water to meet all domestic and industrial demand. As a result, in the outskirts of Bangkok, private and industrial abstraction of groundwater exceeds the safe yield of the aquifer. This accelerates the rate of land subsidence (5-10 cm/year), which in turn aggravates the problem of flooding. Indeed, subsidence has caused some parts of the drainage systems to be below the normal water level and has thus rendered them ineffective.
The minimal discharge to maintain a water level of 1.7 m for navigation (this means 300 m3/s released in the navigation channel from Nakhon Sawan to the Chao Phraya dam, and 80 m3/s downstream of the dam) cannot be maintained because large amounts of water are diverted from the river for dry season irrigation in the northern and central regions. This has reduced the volume of inland waterway transport fivefold between 1978 and 1990. The volumes of water released by the Bhumipol and Sirikit dams are increasingly important to prevent saltwater intrusion, even if they do not meet the navigation demand.
Leptospirosis seems to prevail in flood-prone and irrigation areas, but is under control. There are no clear impacts (positive or negative) of irrigation on health. This is probably the result of a the complicated interaction between socio-economic factors and land use changes. People whose paddy is in irrigation areas are better off economically than those in rainfed areas and hence can afford better health care. Changes in land use transform remote irrigation areas into suburban areas with reasonable road access. As noted above, poverty is less in irrigation areas than in rainfed areas.
During the period 1984-2007 Thailand has 317 513 cases of HIV, resulting in 87 643 deaths. Most HIV cases occur in the services and agriculture sectors in age ranges from 25 to 34 years.
In 1999, the main water-borne diseases were acute diarrhoea (affecting 1.48 percent of the population) dysentery (0.14 percent) and enteric fever (0.03 percent). Malaria, as a water-related disease, affected 0.12 percent of the population.