Milk adulteration is a non bailable offence now. This is good new for Mumbaikars who trust their milk carrier to deliver the milk to them honestly. Both the bag and the bottle can be contaminated by injecting out milk and injecting in water. It goes on in a pretty massive scale all over Mumbai. While this law is probably geared towards the "straight from the cow" private vendors, milk carriers from Aarey to you home do an equal amount of fraud.
If you are having your milk delivered, make sure that you buy from someone who carries that milk straight from the depot to your home. If there is a stop at the milk carriers place for "temporary refrigeration", you can be sure that there is some water going in. If you currently have a milk vendor that takes the milk home, change your vendor. The vendor may also be doing an "exchange" before the milk reaches you, to avoid going home, so you have to watch out for that too. Very difficult to monitor the stuff for the morning delivery though. Watch for word of mouth reviews. It is best to use "non-professional" milk carriers. So your morning servant/part time servant would be a good candidate if they are willing to do it.