Topic
- International regimes 104
- Political parties 102
- Economic development 101
- Precipitation (Meteorology) 98
- Watersheds 98
- Armed Forces 83
- Saline water conversion 76
- Drinking water 75
- Foreign relations 72
- Pipelines 71
- Contamination of environment 70
- Drainage 63
- Health 63
- Water--Purification 63
- Climate 62
- Canals 59
- Wells 58
- Aquifers 57
- Exports 57
- World Bank 57