Radiator water dries 250 ml almost every two days

When my car met with an accident from the front side, I didn't stop and drove my car until it finally stopped after overheating and all this time I was driving keeping AC on. I finally got radiator, condenser, fan assembly replaced and of course head gasket was blown so I had to grind the head and got a new gasket fitted, my car is running fine however I have noticed that radiator water dries but the reservoir tank is always to the mark. Radiator cap was replaced, thermostat valve was replaced, no leakage whatsoever, hose pipes look fine, no sign of water mixing with oil as per the oil stick indication. I got it checked by mechanic he has no clue. I suspect a crack head. What else do u suggest?