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- Water quality 599
- Hydrology 148
- Groundwater 147
- Technology 147
- Irrigation 128
- Contamination of environment 113
- Agriculture 112
- Economics 96
- Sewage 84
- Politics and government 75
- Watersheds 70
- Bureaucracy 66
- Water-supply 64
- Health 60
- Demography 59
- Finance 59
- Saline water conversion 59
- Building 55
- Water consumption 54
- Aquifers 47