While sleeping, the body subsists on less energy. This is particularly true for the digestive system, which is nearly stagnant when we first wake up. When we eat right after waking, our stomach is ill equipped to process everything efficiently and this leads to digestive issues like flatulence and digestive fire.
When first taken in the morning, hot water serves the role of building up digestive fire without taking the system with food. The water gives the digestive system something to process, but the heat in the water ensures that it doesn't put the fire out completely. In addition to the benefits hot water has for digestion, having water on an empty stomach first thing in the morning has a diuretic quality and cleanses the system of any toxins that may have acumulated during sleep.
Eliminate waste (urine, feces) right after waking up.
Heat water on the stovetop to a boil so as to purify the water. Avoid the use of microwaves and other artificial sources of heat.
Consume about a teacup's worth of hot water after it has cooled, or pour a small amount of purified, room temperature water into the cup to cool it off.