1.1.1.WATER RESOURCES Tunisia’s river network is dense in the north where the Medjerda is the most important river. The northern basins provide regular and substantial contributions relative to the rest of the country, supplying 82 per cent of surface water resources. Basins in the centre and south are characterized by low and irregular contributions. The north is also distinguished by its richness in shallow groundwater (in the northeast coastal plains). The centre is relatively well off in deep and shallow groundwater with an average to mediocre quality. The south is characterized by its low potential for renewable groundwater from continental infill (geothermal properties, temperature around 75°C). Natural wetlands, such as sebkhats, lagoons and saline lakes, with a total area of 8,220km2, are characteristics due to the topography, irregular rainfall and arid climate. Sebkhats are most common. These are inland depressions that fill with water in winter and dry in summer; salinity is generally high and variable. Lake Ichkeul (90km2) nature reserve is the most famous. Artificial lakes and dams are starting to grow; their present area is estimated at about 150km2. The internal renewable surface water is estimated as 3.100km3/year and renewable groundwater as 1.495km3/year. As overlap between surface water and groundwater is estimated to be 0.400km3/year, the total annual internal renewable resources would be 4.195km3. Exploitable fossil resources are estimated at 0.650km3. Including surface water and groundwater entering through Algeria, the total renewable water resources are 4.595km3. About 2.100km3 of surface water resources are exploitable through reservoirs. It will be possible in future to increase this through significant work to conserve water and soil systems and groundwater recharge. Renewable groundwater resources can be divided into two categories depending on the depth of the water: •up to 50m, the waters are defined as tables and can be used for private enterprise, albeit with some restrictions (perimeters backup or prohibition). The potential is estimated at 0.745km3, but the volume actually used is 0.780km3/year – a 5 per cent rate of overexploitation; •beyond 50m, deep groundwater is mainly reserved for public use. The potential is estimated at 1.400km3, including 0.650km3 from fossil aquifers in the south. The total capacity of dams with a height of more than 15m is estimated at 2.555km3. The total exploitable resources of Tunisia, currently valued on an average basis, are of the order of 4.245km3. At present, the volume developed by large dams, hillside dams, lakes, boreholes and shallow wells is estimated at 3.598km3, or about 85 per cent of total exploitable resources. The policy of creating large dams is associated with major developments in the fight against floods to protect cities and farmland. The use of unconventional water resources has been considered over the past 30 years. The potential of treated wastewater, currently estimated at 0.148km3/year, is expected to reach 0.385km3 in 2020. Production of desalinated water from brackish groundwater resources in the south is estimated at present at 0.013km3/year, and is intended primarily to supply drinking water to urban centres in the southeast.

1.1.2.WATER USE The total water withdrawal reaches 2.640km3/year, of which 2.165km3/year (82 per cent) is for irrigation. Groundwater constitutes 70 per cent of withdrawals, but is subject to overexploitation in some north-eastern and central regions. In the future, agricultural demands are set to continue to increase,, while maintaining its dominance over other sector uses – irrigation accounts for 80 per cent, drinking water 16 per cent, and industry 4 per cent. A comprehensive programme of water saving irrigation has been carried out since 1995 to control agricultural water consumption and reduce irrigation requirements in the long term.

1.2.WATER QUALITY, ECOSYSTEMS AND HUMAN HEALTH Major environmental problems are health risks from ineffective disposal of toxic and hazardous waste; water pollution from raw sewage; limited natural fresh water resources; deforestation; overgrazing; soil erosion; desertification. Irrigation waters are relatively salty (1.5-4g/L) but the degree of salinization of irrigated soils is not at unsafe levels because of leaching by irrigation water and rainfall. The latter, covering 23 per cent of the area managed, are subject to regular monitoring of salinity, particularly for land that can be affected by the raising of groundwater levels.