According to a survey by Maharashtra Pollution Control Board (MPCB) the water quality index of Mumbai is bad much like air quality index.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/mumbai%E2%80%99s-water-quality-index-bad-air-quality-index
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/free-press-journal-mumbai
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/maharashtra
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/mumbai
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/drinking-water-quality
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/state-pollution-control-board-spcb-0
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/mithi
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/biological-oxygen-demand-bod
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/lakes
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution