Water is by far the best. Definitely do not drink coffee and/or tea before the treatment as this increases the concentration in the stomach and draws the water there to neutralize this concentration. This reduces the amount of water entering the cells, which is obviously not good. So drink iteracare treated water beforehand, then coffee and tea!
Drink warm water before and after, but if you are thirsty during the day you can drink fresh water (iteracare water).