Ground water level mapped at various locations of the city

Chennai has a network of observation wells...

https://timesofindia.indiatimes.com/city/chennai/chennai-records-dip-in-groundwater-level/articleshow/84055513.cms

https://www.researchgate.net/figure/Location-map-of-observation-wells-in-Chennai-The-ground-water-level-data-was-received_fig3_325686228

https://cgwb.gov.in/District_Profile/TamilNadu/chennai.pdf

..."The Minjur Desalination Plant is a reverse osmosis, water desalination plant at Kattupalli village, a northern suburb of Chennai, India, on the coast of the Bay of Bengal that supplies water to the city of Chennai. Built on a 60-acre site, it is the largest desalination plant in India.

Construction works were carried out by the Indian company IVRCL and the Spanish company Abengoa, under the direction of the Project Manager Fernando Portillo Vallés and the Construction Manager Juan Ignacio Jiménez-Velasco, who returned to Europe after the inauguration of the plant to work on renewable energy projects.^[1]

Originally scheduled to be operational by January 2009, the work on the plant was delayed due to Cyclone Nisha in October 2008, which damaged a portion of the completed marine works and destroyed the cofferdam meant for the installation of transition pipes.^[1] The trial runs were completed in June 2010 and the plant was opened in July 2010.^[1]

Water from the plant will be utilized chiefly for industrial purposes such as the Ennore Port and North Chennai Thermal Power Station. However, during droughts, water from the plant will be supplied to the public, serving an estimated population of 1,000,000.^[1]"...

https://en.wikipedia.org/wiki/Minjur_Seawater_Desalination_Plant

https://www.thehindu.com/news/cities/chennai/chennais-fourth-desalination-plant-construction-to-begin-in-january/article65938353.ece