The short answer is water. If tap water is safe in the area you live, then that is perfectly adequate.
The long answer is, it depends. Young kittens need milk, either from their mother or if orphaned/rejected, a milk supplement (if a foster mother can't be found).
Water makes up 70% of your cat's body (just like humans), and is vital for survival. Without water, a cat will quickly dehydrate and die. It is essential for proper kidney function and a healthy urinary tract. Cats from 8 weeks of age can drink water. It should be clean, fresh and changed daily. ALWAYS make sure there is fresh, clean water on hand for your cat to drink.
Encouraging your cat to drink water:
Water needs to be changed every day. On hot days, I will sometimes put a couple of ice cubes into the water bowl to cool it down further. Don't forget, if your cat has access to an outdoor cat enclosure, it is a good idea to provide a second water bowl out there for him to take a drink when he is playing, exploring etc. If you have multiple cats, it is a good idea to have several water dishes.
I recommend using a sturdy, pottery water dish for cats which is difficult to knock over. I also find the pottery dishes keep the water cooler for longer, which is important in the warmer months. The water bowl should be wide enough so that the cat can comfortably drink without the sides touching his whiskers.
If you are having difficulty encouraging your kitten or cat to drink enough water, here are some tips:
- Some cats don't like water that is sitting in a bowl. If you have a cat who seems to like drinking from a running tap, a solution that works for many is a cat water fountain. These are electronic devices in which the water re-circulates, oxygenating it and reducing standing time, which leads to stagnation. Some water fountains will also filter the water at the same time. There are a number of popular brands of water fountain on the market.
- Move the water bowl. Some cats don't like their water bowl too close to the food bowl, so try moving it a little further away. Also, make sure it isn't too close to the litter tray. Cats do not like to eat and drink near where they go to the toilet.
What shouldn't cats drink:
Cats should not be given cow's milk to drink as most cats suffer from an intolerance to the lactose in milk and it can cause digestive problems. If you do want to give your cat milk, you can buy specially formulated "cat milk" from most supermarkets or pet shops.
It goes without saying that cats should not be given anything to drink other than water or the appropriate type of milk. Fizzy drinks, alcohol, juice, tea, coffee etc., should never be given to your cat.
If you have a fish tank, cover it up. The chemicals in the water are not good for your cat.
Don't let your cat drink from the toilet bowl. Not only is it at risk of falling in and drowning, but the chemicals and bacteria will make your cat sick.
So to summarise, the only drinks your cat require are fresh, clean water for kittens over 8 weeks of age, or appropriate "cat milk". If you choose to give your cat milk, it is still important to provide it with fresh drinking water in addition. Cat milk can go off quickly, especially in summer, and shouldn't be left sitting out all day. Put a small amount in a bowl, let your cat have a drink and discard any remaining milk after 30-60 minutes. Leave water out 24/7.
Thanks to Lynne for the use of her photo