is it correct?

Drinking purely soda and no water will dehydrate you and is very unhealthy. Not to mention it will make you fat very quickly. Your friend needs water, the body requires it. If your friend doesn't change this bad habit, their health will slowly deteriorate.

You and your friend need to consider lowering your soda intake. Soda has a lot of sugar content. When I was younger I used to consume Coke every day. In my last year of High School, my school banned selling soda at our cafeteria. I learned how to control my intake until I reached a point where I don't crave it anymore. When I stopped drinking soda, my asthma attacks became few and far in between. My eye sight is superior (vs my brother who became diabetic at the age of 14 due to his addiction to Coca Cola who has poor eyesight). My teeth do not have cavities and tartar. If you must drink cola, consider the diet ones. It's a start. Try to switch to diet or zero then eventually lower your intake every day.

Try this sometime. If you have a 'baby tooth' (a milk tooth which was shed when the adult tooth grows) or even a small piece of chicken bone or similar, leave it in a glass of coke overnight. Look at it in the morning (if you can find it) and think what the same liquid does to your teeth and stomach over time!

I personally can't stand Coca-Cola, I think it's really gross. It's not good for someone to drink only soda and no water. Soda is full of sugar, sodium and other additives. Without drinking water, you're likely to get dehydrated. But if he is living an otherwise generally healthy life, eating good food and getting good exercise and maybe even getting hydration from other sources, then he should be fine. It's not good but it's not exactly bad, either.

Jeah definitely, Your friend can see the result in the long run. I do like coca cola too, I drink it everyday without fail. It has been my habit and sometimes I forget to drink water. I can feel the negative side effects and I dont really have to wait for a long time. If I drink too much like four times a day, I usually got my sore throat. It means that we should take everything in moderation.