OMGoodness!
Thank you - both
Kacey - I don't actually remember what I did. I was just pootling around experimenting with different layer effects and transparencies and just scribbling, erasing and smudging in various shades of white green and blue on different layers, over the generally pink green and purple plasma space background that I started with... In fact I'd stopped caring about it by then because I was already feeling quite miserable that I'd failed to get it right, when it all just kind of... happened.
In truth, though - its not really water at all.
If you look at any photograph of real water you will see that what I've done isn't anything remotely like it. By loosing myself in a low mood I seem to have accidentally discovered some sort of essence of how I feel about water, and expressed it as a substitute for the real thing... if that makes any sense?
I suspect that this strange illusion isn't going to work for everyone - only for people who have the same or similar feelings about water as I do.