This happened in my S2 but it was a fooked water pump, just leaked all the water out.

I check mine before evey journey but this one time I was only going to blockbusters and when I got a mile down the road I thought "This is warming up quick" and the needle didn't stop filled it with water to drive home and it was ok but obviously leaked out again over night.

What car is it? Water pumps usually aint that expensive and its a good excuse to change cam belt too