You could try particle systems. Trapcode Particular would be pretty good at doing this. It's a paid 3rd party plugin. You may also try and use the CC Particle world that comes with AE in conjunction with turbulent displace. You need several copies with different settings.
I'll give that a try, thanks.
You could also use stock footage like this one:
If you go for a 3rd party plugin, Boris FX also has a solution:
(the tutorial is in Premiere, but the plugin also works inside AE)