Best startup idea addresses the need of its customers. One of the dire need of Indian Central and state governments is keeping cities clean. It is quite an impossible task to do it in full scale. Also takes a lot of maintenance cost and effort. Indian tourism industry heavily suffers from dust pollution.
Based on this requirement, one of the best startup ideas will remove dust off the roads of India. If you can come up with a technology that can efficiently clean the roads, stations, platforms etc and maintain like an airport, that is a huge achievement. Many governments are ready to pay you hugely for this service.
Artificial raining is one of the solutions for roads. There are machines that can do street sweeping, absorb dust and other minutiae and clean them. One can propose a contract with the governments to keep cities clean and buy trucks of that sort.