The exact temperature of a glass of water in degrees Celsius

The temperature of water in a glass if room temperature is 21 degrees Celsius if a glass is standing one in that room, because room temperature is commonly given as 20 to 22 degrees Celsius, however, if the air in the room goes through temperature variations, then a body of water will heat up or cool down, then the temperature of the water in the glass tends to average out those temperature variations.