The reason why you should drink a glass of water before having tea or coffee is that it decreases the acidic levels in the stomach. Tea has a pH value of around 6 (which is acidic), and coffee has a pH value of 5 (which also falls under the acidic range). So when you drink tea or coffee, be it morning or evening, it can increase acidity and might increase the risk of acute illnesses ulcers and also cancer. If you drink water before tea or coffee, it not only dilutes acid levels in the stomach nut also minimises the damage on the stomach and overall health. It also lowers the effect of tea on the teeth due to its high acidic levels. Drinking water also keeps the body hydrated and aid in flushing toxins from the body.