smoke/steam coming fron air vents

[Nware]

i was driving my 325i today and after about 7 or 8 miles smoke/steam started coming out of the air vent with got worst fast. so i pulled over my temp was just below half way, so i opened the bonnet every thing seemed normal the engine wasnt that got there was no smell from the engine just my coolant was alittle low but not to bad. so i drove to my mums house about 500m away and the smoke got abit worse so i stopped there for 30 mins put about 1litre of water in drove back from with is 3 miles away and it didnt smoke at all?

its pretty weird hope someone can help
cheers

[suedenim]

Sounds like your heater matrix may have given up, maybe resulting in an air lock, hence why it stopped steaming. I wouldn't drive it until I was sure of what was what.

[JF008]

See if the driver's footwell is wet , take the sill cover off and stick your hand under the carpet. If you lost coolant it has gone somewhere surely

Edit: Passenger foot well