What is better to give the cat to drink - milk or water - is important and you can distinguish several key points:

1. Water:
Mandatory: Water is the main and most important drink for cats. They are essential for their health and the proper functioning of the body.
Functions: Water helps maintain the balance of fluids in the body, aids digestion, and provides support for kidney function.
Recommendation: The cat must be offered fresh and clean water at all times. You should refresh the water at least once a day and clean the bowl regularly.

2. Milk:
Myth: There is a common perception that cats like milk. It is true that some cats can find milk palatable, but the essential facts must be considered.
Lactose: Most adult cats are lactose intolerant, meaning they have difficulty digesting lactose (the sugar found in milk). This is because their body stops producing the enzyme "lactase" that breaks down lactose.
Symptoms: drinking milk can cause digestive problems such as diarrhea, stomach aches and the like.
For young cats: young cats (kittens) can drink mother's milk, but as soon as they start eating solid food, the milk should be stopped.

3. Additions to milk:
If you have a cat that really likes milk, there are now special types of milk for cats that are lactose-free. Such milk can be a good option if you want to give the cat a drinking experience that will not cause digestive problems.
4. The importance of water:
Cats that get adequate water from not only liquid sources (like wet food) are less prone to kidney problems.
It is important to encourage the cat to drink water, especially if it only eats dry food. You can consider using running water sources (a well or dedicated devices) to encourage drinking.

Summary:
Water is the best choice for a cat. Milk, although it may be tasty for some cats, is not a necessary food and may cause digestive problems in most. If you're worried that your cat isn't drinking enough, consider a variety of ways to encourage him to drink water, including using wet food or running water sources.