Sallylou has the right idea if you want to quit.
I have had coffee all of my life. We first had kiddie coffee which is half milk with sugar and were weaned to adult coffee. My doctor made me cut back. Still have one cup (mug which is actually two cups) every single morning. I do not wish to quit because I love the stuff.
Still, it is better for your health to drink water as Jiro suggested.
I have discovered that the word "diet" begins with d i e.