My Vauxhall Astra is loosing water its a 1.4i 07 plate. When I top the water up after a few days its empty. I have had 3 mechanics look at it. It has been pressure tested and is fine the head gasket and water pump is fine no leak or white creamy stuff loads of mechanics have had a look at the car and is unable to locate a leak anywhere, I need some advice what to try next where is this water going the car is not over heating I have also put a brand new radiator cap on.

This is doing my head in as all mechanics are saying its fine but it is loosing water.