People in different states in India speak different languages. I am living in a southern state called Karnataka (pronounced Kur-not-ah-kah) and the main language spoken here is Kannada (pronounced Kun-uh-dah). Bangalore, however, is a cosmopolitan city, so people come here from all over India. Thus, another major Indian language spoken here is Hindi (prononced Hin-dhee), which is commonly used in the northern regions of India.
We use rupees (pronounced roo-pees). Currently, 70 rupees is the equivalent of 1 US dollar. India is a much more cash-based economy than the U.S., meaning that people usually use cash instead of credit cards or debit cards to pay for daily needs.
A bottle of water costs around 40 rupees. However, most of the time I just drink water from the water filtration systems located around the campus of the National Centre for Biological Sciences, where I live and work. The raw tap water in India is often filled with bacteria and pollutants, so it is not safe to drink.