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Topic
- Water quality 91
- Agriculture 28
- Groundwater 28
- Irrigation 27
- Technology 23
- Contamination of environment 17
- Watersheds 17
- Hydrology 10
- Sewage 10
- Water-supply 10
- Soils 8
- Water consumption 8
- Aquifers 7
- Economics 7
- Finance 7
- Saline water conversion 7
- Sewage--Purification 7
- Deserts 6
- Bureaucracy 5
- Demography 5