sushubh- I wouldn't compare internet bandwidth with water. Clean water is a finite resource, doesn't matter how you use it, it will get over.
However, internet bandwidth is a man-limited resource. You have 100mbit in japan. Whether they use 40mbit at a time or 4mbit doesn't faze the ISP. This is because the optic fibre is already laid and fiber optic cable has a capacity of 1000
gigabit/s. The only limiting factor in this equation is internet
routers. And you can make a connection OC-3 to OC-48 to OC-155 to OC-192 by simply changing(upgrading) your internet router on both ends of the optic fiber. The fibre optic remains the same. The cost of such routers drop drastically as time goes on. In the early 90's, OC-3(155mbit) was costly as hell. Now transoceanic OC-192(9900 mbit) costs less than OC-3.
When bsnl and shortsighted govt policies force an artifical shortage of bandwidth on consumers, its not the consumers who are at fault here. So many countries provide 3mbit, 20mbit, 50mbit etc. Is bandwidth in those countries drying up? Its the content that is the limiting factor.
Recall the telephone situation in India 3-4 years back. Prices for landline equipment in exchanges and mobile tower equipment installed on rooftops have not fallen much from what they were in 2000. But telephone prices have crashed 80-90 %? Why such a discrepancy? Govt policies. Artificial shortage.