1- There is thousand ships cross Malaca strait, is India gonna stop each ship to identify which one belong to China?
, attack chinese ships in internatinal water will only invite retaliation. The worst nightmare for India is that it mistakenly attack otehr nations or U.S merchant cargo
than we chinese will have free ticket home, India will have to deal wtih U.S 5th fleet and others.
2-What make you think that India is capable to set blockage or more likely the other way around, India navy only take on small countries, with China you have think twice of your misadventure or all your ships will be at the bottom of Abyss at the vincinity of your sea ports.
3-let assume that India is sucessifully to set blockage to Chinese oil cargo, we still have pipelines from central Asians and Russia, beside that we have oil field in Xinjiang operational, we will be able to survive with "some inconvenient", but if Chinese divert water for few days, not only millions but hundred millions Indians will suffer from dehydration, without saying your economies will scrumbled (agriculture,farming, industries), Indians social life will on total chaos: Indian people will fight to death among themself to get water.
try not to drink for one day...than come back to arg with me which one is more important ? water or oil.