Meet Mr. Shyamsundar and Pankajam, a couple who have been using this well water for the past 25 years for all purposes-including drinking. The well is about 3ft dia and 40ft deep. The well had water at ~30ft from the ground-so almost 10ft of standing water. They got cauvery connection but disconnected it since the pressure was not enough to reach their sump. They closed off the sump too after some years. They are dependent only on this well water. Also started doing rooftop rainwater harvesting and are diverting the water into this open well after filtration. They haven't tested the water for quite sometime but they say that 'the water is good and we haven't encountered any health issues so far'.
They also told and showed couple of open wells in their neighborhood. Borewells dug 200ft deeper in the neighborhood are getting muddy water. Open wells 40-80ft deep have good water. Majority of the houses are using that water for some purposes.