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Historically, Bahrain has utilized groundwater for both agricultural and municipal requirements. Natural freshwater springs used to flow freely in the northern part of Bahrain and before 1925 the water supply depended on these springs and some hand-dug wells, the total discharge of which was estimated at 93 million m3/year. With increased water demand after the exploration of offshore reservoirs of crude oil and gas in 1946, spring flow decreased and water started being pumped from boreholes. During the 1980s, most of the springs ceased flowing, and increased demand for water caused deterioration in water quality, including the intrusion of seawater into the aquifer system (UNU, 1995). In 1988, groundwater use in Bahrain was estimated to be 153 million m3/year, including 138 million m3 of tube-well abstraction, 8.1 million m3 of water from land springs, and 6.6 million m3 of water from marine springs.
In 2003, total water withdrawal in Bahrain was 357.4 million m3 (Table 3 and Figure 1). The part used for irrigation and livestock watering purposes dropped to 45 percent whereas it was 56 percent in 1991. Total annual water demand was met by three sources: primary groundwater (238.7 million m3), desalinated water (102.4 million m3) and treated sewage effluent (16.3 million m3) (Table 4 and Figure 2). This means that non-conventional water sources accounted for 34 percent of total water withdrawal in 2003. About 90 percent of the water used in agriculture, including livestock, was primary groundwater and 10 percent treated wastewater. For municipal and industrial purposes about 48 percent of the water used was primary groundwater and the remaining part was desalinated water.
The total freshawater withdrawal (primary groundwater plus reused treated wastewater) represented 220 percent of the total renewable water resources in 2003, meaning that abstraction of fossil water and groundwater mining was taking place. The excessive pumping of groundwater caused a sharp decrease in groundwater storage and a reduction in potentiometric levels of about 4 meters between 1965 and 1992. As a result, more than half the original groundwater reservoir has been completely degraded due to seawater intrusion and saline water up-flow from the deeper zones. Table 5 shows that annual extraction is almost twice the annual recharge, leading to an ever-increasing groundwater deficit. While the average annual groundwater depletion over the period 1965-1992 was approximately 40 million m3, in 1991/92 it was over 96 million m3.
In 2003, the total quantity of desalinated water used was 102.4 million m3 against 44.1 million m3 in 1991. In 2005 treated wastewater amounted to about 62 million m3/year of wastewater (secondary treatment) against about 45 million m3 in 1991. Despite an increase of 100 percent compared with 1991, only 16.3 million m3/year received tertiary treatment and part was used for irrigation purposes in government farms and some private farms, while the rest was discharged to the sea. The chemical and hygienic properties of the tertiary treated water are within international limits and are considered good for agricultural purposes. Although the government has plans for the full utilization of Treated Sewage Effluent (TSE) water through major agricultural projects, delays and lack of funds for these projects have limited the use of these waters.