Guido,
I would say that the best way of finding out whether or not aparticular combination of paints and varnishes work together is to try them out on a test piece before using them for real. OK, unless you are prepared to wait for a very long time this won't catch any long term issues, but you will at least find out if one product dissolves another, won't give a good key for subseqent layers, peels off, starts to crack or produces some other fairly immediate compatibility problem.
Vallejo is a much-used brand in plastic modelling circles, and consequently has very good distribution, so their paints and varnishes should be reasonably easy to find no matter where you are. Try looking in shops/webshops that cater for the plastic kit air and armour crowds rather than the model boat specialist vendors. Also take note of the difference between Vallejo Model Color, which is intended for brush application, and Vallejo Model Air, which has been formulated to suit airbrush painting. They can both be used the other way around, but are not all that well suited for such cross-over techniques, so pick the one that'll fit your preferred method of painting the best.
Vallejo also do a series called RC Premium, which is primarily intended for painting r/c car bodies; however, the PU gloss varnish from this series is a really nice product that works equally well with brush and airbrush, hs excellent self-levelling qualities and produces a very nice and glossy finish.
As you may have gathered from the above, I am a great fan of Vallejo when it comes to acrylic paints. However, I have no personal experience of the acrylic water, i.e. their range of water effects (see **LINK**). As far as I understand, these are not really paints but rather imitation water, i.e. intended to be laid with a certain depth over a painted surface to create the illusion of water. There are, to my knowledge, several types of such fake waters available, and I think you might be able to find more information on websites and fora dedicated to model railways and dioramas, both of which are into the recreation of landscape features such as water.
/Mattias
Edited By Banjoman on 16/02/2015 14:34:35