The first episode of H2O is Metamorphosis, where the girls (Cleo, Emma and Rikki) visit the mysterious Mako Island and turn into mermaids when they enter the moon lake during a full moon.
Metamorphis
Season 2, episode 2: "Control"
The awakening
It's explode 1
The episode you are referring to is "The Denman Affair," which is the 11th episode of the first season of H2O: Just Add Water. Will sees Bella transform into a mermaid for the first time during this episode.
H2o is on tv episode 1 and 2 episode 3 should come soon but episode 4 is if number 3 is succsesful
It's episode 78, "Graduation."
Bella kisses Will in the "Just Add Pluots" episode of H2O: Just Add Water. This episode is part of Season 2 of the show.
They just came out with new episodes of h2o I think a season 4!!
the finale
http://vids.tv/H2O-Just-Add-Water/tv/season-2/episode-12-Monster
The last episode of H2O:Just add water is season 3 episode 26 and it is called graduation.