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- Water quality 109
- Irrigation 29
- Finance 22
- Agriculture 20
- Groundwater 18
- Sewage 17
- Contamination of environment 16
- Hydrology 15
- Demography 14
- Drinking water 14
- Technology 13
- Building 12
- Bureaucracy 12
- Health 12
- Water--Purification 11
- Aswan High Dam (Egypt) 10
- Water-supply 10
- Politics and government 9
- Soils 9
- Watersheds 9