what usually works for me is this recipe -
2 parts PVA glue
2 parts gloss varnish (I use the stuff you would varnish, say, a bench with, rather than the one that Games Workshop makes)
1 part distilled water (it is important to use distilled water because you don't get the minerals from the tap into the water effects).
This is thin enough so it will apply nicely to a base, but thick enough so that it doesn't flood over the edge (not a problem if you are uiong a Warmachine base!)
If you are using pre-thinned PVA glue, don't bother with the distilled water - it will be too runny!
If you want to make waves -
2 parts PVA glue
2 parts gloss Varnish
1 part white gloss house paint.
This recipe is a bit thicker and you can tease it up to make waves. If you wanted to, you could add some fine sand to get that foamy texture. Never tried this, but hey, you could always experiment.
For tinting, either paint the surface that you want to be tinted, then coat it with water effects, or use ENAMEL paint. Don't try to mix anything for the wave Water Effects, and don't mix acrylic paint with the Standard stuff.