Not where I'm from either (Chennai, though my dad is from Thanjavur), but in the area around the Gangetic plain, this might be a common practice, and it is deleterious to humans and the environment.

understood, however if someone upstream poisons their water supply, be it farm/agriculture, industrial runoff, etc.. it still effects you and your family downstream. If there is too much, everything starts to deteriorate.

Sure. People living there would be affected. But i don't know common those practices are. Might be just North India. I am from South. There are many difference between North and South states and within Southern states and districts.