1.1.1.WATER RESOURCES With an average width of 120km, Costa Rica receives about 170km3 from rain and about 75km3 finds its way into rivers and lakes; another 37km3 ends up in underground aquifers. The remaining water is lost through evaporation and evapotranspiration. Costa Rica is divided into three major slopes or basins: •the Atlantic side is the wet and rainy side and rarely experiences a deficit of water throughout the year; •the Atlantic side incorporates the northern slope, which drains into the San Juan river bordering Nicaragua and also towards the Caribbean Sea. The sub-basins within this slope contribute 5.8km3 annually to Lake Nicaragua and more than half of the water that flows into the San Juan river (around 23.2km3); •the Pacific slope is drier with a shared decline in average flow during the dry season. In total, there are 34 principal drainage basins in Costa Rica, with 17 having a major sloping contour. They range in size from 207km2 to 5,084km2. Groundwater is the primary water source in Costa Rica, where it accounts for nearly 90 per cent of agricultural, industrial and domestic water demands (with the exception of hydroelectric generation). Volcanic activity has formed highly permeable subterranean layers within the fragmented igneous lava. This phenomenon, coupled with high rainfall, has created aquifers in the central and northern part of Costa Rica’s Central Valley, where more than half of the population lives. These aquifers are called the Upper and Lower Colima and are separated by a layer that acts as a semi-permeable aquitard, which allows the descending and ascending vertical transfer of water. It has been estimated that the Lower Colima extends for approximately 230km2 and that the Upper Colima spreads over approximately 170km2. The Upper Colima aquifer is recharged from the Barva and La Libertad aquifers by vertical percolation. The Upper Colima also receives a large part of its recharge from rain infiltration in those areas where there are no overlying smaller aquifers. The Lower Colima is recharged from the Upper Colima by vertical percolation and from surface water where the Upper Colima is absent. The average recharge of the aquifer system was calculated in 1990 at 8200L/s. The depth of the water table level varies, depending on the surface topographical irregularities, but generally it ranges between 50 and 100m. The direction of the underground flow is from northeast to southwest in both aquifers. Surface water is represented by approximately 13 major rivers, with many adjoining tributaries that range in length from 50 to 160km. Costa Rica's major reservoir is Lake Arenal.

1.1.2.WATER USE In general, water quality is acceptable for drinking in urban areas as well as many rural areas. The government of Costa Rica understands tourism to be the primary driver of the national economy; therefore, great attention has been paid to improving potable water systems throughout the country. Costa Rica has the highest demand of water, both in total and per capita measures, in Central America. Per capita water usage is about 1,860L/day, amounting to 5 per cent of total available groundwater and surfacewater. Other Central American countries use an average of 3 per cent of total supplies. About 60 per cent of the Costa Rican population lives in urban areas; therefore, considerable emphasis has been placed on expanding water services to cities over the last decade. Approximately 99 per cent of the urban population is connected to water services, which is higher than the 90 per cent average for the rest of Latin America. Connection to the public water supply in rural areas of Costa Rica is about 92 per cent, representing about 1.56 million inhabitants. Agriculture accounts for 6.5 per cent of Costa Rica's GDP and 14 per cent of the workforce. Costa Rica irrigates around 21 per cent of its land under cultivation, relying primarily on surface water. The irrigation sector is managed by the National Irrigation and Drainage Service (SENARA). Two irrigation districts of note that differ in size and method are: •the Arenal-Tempisque Irrigation District (DRAT), which grows staple crops; •the Irrigation and Drainage of Small Areas (PARD), which is smaller but benefits more families than DRAT and focuses on higher-value crops. The Arenal-Tempisque Irrigation District (DRAT) is located in Guanacaste province, the driest area of the country (during five months of the year), and is nearly 100 per cent supplied by surface water, utilizing water from Lake Arenal. The DRAT has increased its surface area from 100km2 in 2003, to 280km2 today. It benefits approximately 1,125 families, producing mainly sugar cane, fodder, rice and fish (4km2 of aquaculture), generating income of approximately US$163.7 million from this region. The producers in the area pay SENARA a fixed rate fee of US$42.5/ha/year for water used in irrigation. Financial resources of US$13.7 million are being negotiated for the expansion of DRAT. The Irrigation and Drainage of Small Areas (PARD) is a district promoted by SENARA and is a response to requests made by individual producers, associations of producers and state institutions. SENARA is in charge of constructing irrigation canals. These are not state properties; they belong to the producers, who are responsible for properly maintaining the irrigation system. The PARD encompasses an area of 27km2 and benefits 2,023 families, who mainly cultivate vegetables, root crops, tubers, decorative plants and prickly pears. The areas where the DRAT and PARD operate include approximately 307km2; the total water demand is estimated at 35.2m3/s. Of this total demand, the Ministry of Environment and Energy Country Overview - Costa Rica (MINAE) has granted 1,240 concessions for exploiting surface and groundwaters for agricultural use; however, less than 97 per cent of the water in Costa Rica utilized for irrigation comes from surfacewater. According to the most recent figures published by FAO, Costa Rica theoretically has the potential to generate 25,400MW; however, more practically, the potential is closer to 10,000MW. The Lake Arenal has approximately 1,570BCM of useful capacity and produces roughly 70 per cent of Costa Rica’s electricity. The hydroelectric dam on this lake is known as the Presa Sangregado Dam, the Arenal Dam or the Sangregado Dam. The dam generates 640GWh/year and is located on the southeast shore of Lake Arenal in the Guanacaste Province, northwest Costa Rica. The Arenal hydroelectric project is operated by Instituto Costarricense de Electricidad. Other important hydroelectric operations in Costa Rica include the Cachí (three 34MW turbines), Angostura (three 70MW turbines) and Corobici (730GWh/year), which is a component of the Arenal hydroelectric project.

1.2.WATER QUALITY, ECOSYSTEMS AND HUMAN HEALTH Costa Rica’s major environmental problems are: deforestation and land use change, largely a result of the clearing of land for cattle ranching and agriculture; soil erosion; coastal marine pollution; fisheries protection; solid waste management; and air pollution. While drinking water is good in many parts of the country, there are still many concerns about the quality of water in streams and lakes. It has been observed that surface water pollution is a threefold problem. Untreated effluents from urban wastewater (only 3 per cent of wastewaters receive treatment) account for 20 per cent of the problem; 40 per cent comes from solid waste and industrial effluents (heavy metals being the primary culprit) and 40 per cent from the agricultural sector. In the agriculture sector alone, 70 per cent of pollution comes from debris from coffee plantations. Water basins that receive large quantities of contaminated runoff include the Grande de Tárcoles and Large Terraba rivers.