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- Water quality 776
- Hydrology 165
- Groundwater 159
- Technology 154
- Irrigation 133
- Contamination of environment 124
- Agriculture 114
- Economics 101
- Sewage 88
- Water-supply 81
- Politics and government 76
- Watersheds 74
- Bureaucracy 71
- Demography 62
- Finance 62
- Health 62
- Saline water conversion 62
- Natural resources--Co-management 59
- Building 57
- Water consumption 57