Survey samples a sliver of blocks in each State and counts how many blocks have critically low levels of water
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/groundwater-reserves-estimate-be-updated-soon
[2] http://admin.indiaenvironmentportal.org.in/category/author/jacob-koshy
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/hindu-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/groundwater
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/central-groundwater-board-cgwb
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rivers
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources