SEAT Ibiza III - Coolant Leak - SWM

I've a 2006 Seat Ibiza Stylance, 1390CC Petrol, 5DR, Manual which has a slow coolant leak.
Loses about 750ml after a 3 or 4 short runs 3-4 miles or after a long run > 30 miles.
Can't see any puddles or any visible wet patches.
It's done about 45,000 miles.
Any suggestions as to how to locate the problem?

SEAT Ibiza III - Coolant Leak - Peter.N.

Have a look around the header tank filler cap and overflow pipe for signs of dry antifreeze or put the overflow pipe into a receptical while being driven to check if the water is being blown out, a leaky head gasket will cause this.

SEAT Ibiza III - Coolant Leak - SWM

Thanks I had a look but no evidence of dry antifreeze. But the leak got progressively worse & so needed a garage to look at it. They found that a plastic manifold attached to the head had a fine crack in it, replaced this (a SEAT part) and the 2 hoses to it and it's ok now.