Coolant question

[tacticalx86]

Went to start my BMW 320i F30 early this morning and had a message saying engine coolant level too low. However, the message then went off. I did check and it does look low, added some water in the meantime but just wondering why it would be low in the first place as there's no evidence of a leak? Certainly not from the outside. And I don't know why the message would then go away.

 

[tacticalx86]

It should be a sealed system so if it's disappearing then there's definitely a leak somewhere. That or your HG is on it's way out, but I don't think that's overly common these days.

Doesn't it over the years get lower though? It's 12 years old and I'm not sure if its ever had a major service.