Rover 25 engine smoking

Hi, the other day my car cut out on me and stopped dead in the road. i managed to restart the car after 20 minutes, to get myself to work, i then checked the engine and it had started to smoke i checked my water level and that had gone and my oil was low but not below the minimum level. i filled both of these up then left it for a few hours while i was at work, after i got home which is only a 10 minute drive the engine was smoking again. i checked the levels again and needed to fill the water tank up, there is no leak with the water tank or with my oil. i have checked to see if there is white/cream gunge in the water tank and in the oil tank but there is nothing. after the engine stops i get a hissing sound that sounds like it is coming from the radiator hose or from the actual oil tank but cant see any leaks, its just air that comes out once the engine has stopped. Please Help!!!!!