car has only done 750 miles gave it some stick in second 7k rpm changed to third noticed what looked like a big puff of smoke, after looked at the back of the car only to find lots of water all over the back with little black specs in (oil unburnt fuel ?) i have noticed several times little pools of water in the tail pipes. the car was fully warmed up and the temp outside was 10 deg. dry day, is this just water build up (ps i do a lot of short journeys)