coolant query

[mand]

Hi my 1992 vr6 has had the old green coolant changed to the pink stuff several months ago. I noticed that the coolant level is now about 1.5cm below minimum. No leaks found yet. Is this drop acceptable??
Also is it ok to top up this small loss with just water and tap or distilled.
Wanted to check before I do something stoopid!
Cheers
Mand