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- Water quality 603
- Groundwater 149
- Hydrology 149
- Technology 148
- Irrigation 129
- Contamination of environment 115
- Agriculture 112
- Economics 96
- Sewage 85
- Politics and government 75
- Watersheds 70
- Bureaucracy 66
- Water-supply 64
- Demography 60
- Finance 60
- Health 60
- Saline water conversion 59
- Building 55
- Water consumption 54
- Aquifers 48
