Tanks are integral part of temples and devotees believe a dip in these holy waterbodies will absolve them of their sins.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/pollution-level-high-temple-tanks-kanyakumari
[2] http://admin.indiaenvironmentportal.org.in/category/author/b-kolappan
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/hindu-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/tamil-nadu
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/religious-places
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/urbanisation
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/kanniyakumari
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution