I am happy with four litres of plain water every day. However, the quantity we need varies with each person. Do what works for you. Do what you can to get the purest water possible. I like to keep it real.
Water is a bit magical for me. It is an element which can be influenced, like the Japanese scientist Masaru Emoto proved.
Thus, I like to add a few drops of Bach flower essences to give my water a beautiful energy.
Drinking water in small quantities and regularly throughout the day helped me to recover after my teeth enamel was badly damaged. For many years, I did grind my teeth so much because it was a way to cope with the abuse.
Lastly, Renegate Beauty by Nadine Artemis is a must-read, notably as regard to the information about water.