The Delhi government doesn't have data on implementation of rainwater harvesting systems in city buildings, departments or flyovers.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/no-data-harvesting-rain-ngt-forms-panel
[2] http://admin.indiaenvironmentportal.org.in/category/author/abhinav-garg-t
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/times-india-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-harvesting
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/buildings
[7] http://admin.indiaenvironmentportal.org.in/thesaurus/national-green-tribunal-ngt
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi-pollution-control-committee-dpcc
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi-jal-board-djb
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rainfall
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources