SMORG wrote:
All Citadel paints are designed to work either way.
Two things to consider:
The idea is that base paints, or foundations as they used to be called, are designed to get better coverage over dark by having different pigments.
The reason you add water is to make I smoother rather than go further. If you use it straight you will find it tends to dry out quickly and is normally too thick to not obscure detail.
Hope that helps
Prettymuch what SMORG said.
I also sometimes thin them down as I find thick foundation paints sometimes clog up detail. But yeah, unless you are painting highly contrasting colours (blue over white for example) I would almost always water them down before using them.