Ask the vet - Cat
Is it OK for cats to drink milk?
Vet at FirstVet answers:
The cat’s gastrointestinal tract is not made to drink cow’s milk; cats are lactose intolerant. It is neither necessary nor appropriate for cats to drink milk.
Many cats like milk and seem to tolerate drinking it, while others can get stomach pains and diarrhoea. There are some discussions regarding cats drinking lactose free milk instead, but it is still not recommended. Cats should drink water!