It is neither terrorism nor natural disasters but the unavailability of safe drinking water which leads to the highest number of deaths in Pakistan.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/unsafe-water-kills-most-pakistanis
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/world-bulletin
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-supply
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-quality
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pakistan
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/south-asia
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/waterborne-diseases