Was the refrigerator just installed?
It can take up to twenty four (24) hours for the water to properly chill after installation.
Was a large amount of water just dispensed?
If a large amount of water was just dispensed, it will deplete the water reservoir. The new water needs time to chill.
Is the dispenser being used regularly?
If water is not being used very often the first glass of water may not be as chilled. Discard the first glass of water.
Is the refrigerator connected to a cold water supply line?
Verify the unit has been connected to the cold water line. Installing the refrigerator to the hot water line will cause the unit to dispense warm/hot water.