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- Water quality 60
- Hydrology 25
- Economics 20
- Groundwater 19
- Politics and government 19
- Demography 16
- Irrigation 14
- Aquifers 13
- Saline water conversion 12
- Agriculture 11
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- Bureaucracy 7
- Resource allocation 7
- Precipitation (Meteorology) 6
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- Peace 5
