Skoda Octavia 2007 about 135k miles.    Water pump has never been replaced as a cambelt. Last time coolant was changed was about 14 months ago.

While driving about at 70 mph about 6 weeks ago the coolant levels dropped -topped 250 millilitre and it made sound of air coming out.

Then after 2 weeks again, levels again dropped and had to top up about 400 mills

The temp gauge has always been at 90.

While looking visually for leaks, there are stains on the water pump, that may suggest that water pump may be leaking under pressure. Rest appears okay. I took it to a garage and they said that it could be water pump as there is lot of stain on it and suggested replacement.

But, since topping up last time then, I have done about 550 miles and the coolant level has not fallen at all. I am bit confused as to why the coolant level has not fallen again and should I replace water pump?

 

Can the coolnat level drop and then be steady ?.

The only explanation - could it be that somehow airbubbles were generated ?

Are you filling to MAX then it is dropping to MIN or going below MIN?

 

Do not fill to MAX as not necessary if it finds it's own level and stays there. 

 

It sounds like you will have to do something sooner rather than later if you do have a drop in Coolant again. 

The staining confirms a leak and it is conceivable that it was then plugged over time by debris in the coolant, this may or may not last.

 

The bottom line is it's had/has a leak and needs fixed.

Is it advisable to have the camchain replaced with the water pump or it doesn't need to be?