1999 Nissan Altima White Smoke Iol Coming Out Te Tail Pipe Fix

i looked under the car and noticed that there is water under the front part of the engine, i looked at the head gaskit and it seemed to be ok, i aslo checked the radiator and it looked full bit i squeezed the radiator hose and didn't hear the water flow thats when i looked under the car. If you could help me ot that wold be great thank you, Patrick