In the start of the show H2O: Just Add Water, there are three normal girls who get stranded on the magical and mysterious Mako Island. After a while they end up in a cave there. It's not a normal cave though. It's the moon pool which turns them all into mermaids.
Whenever they get wet, 10 seconds later they are mermaids!
In the show they struggle to keep from getting exposed, but sometimes they use their powers on humans such as Cleo making her sister's water bottle squirt on her.
Here is our list of characters:
- Emma Gilbert - She is best friends with Cleo Sertori and Rikki Chadwick. She has a confident and responsible, if somewhat controlling, personality. She has the ability to freeze water, and later develops the ability to manipulate clouds, ice, and snow.
- Cleo Sertori - At first she was shy and a little awkward, but eventually became outgoing and personable. She is able to manipulate and mold the form of water, as well as increase or decrease the amount of water present. She is later able to control the wind. She is best friends with Emma Gilbert and Rikki Chadwick.
- Rikki Chadwick - She is the new girl in town at the start of the show, who tends to be aloof and rebellious. Her power is the ability to manipulate heat in water, ranging from warming to boiling, which eventually grows to allow control over fire and lightning. Best friends with Emma Gilbert and Cleo Sertori.
- Lewis McCartney - Cleo's childhood friend who is academically gifted and thinks of himself as a scientist. The girls tell him of their secret and he works to understand why the transformations occur between human and mermaid.
- Charlotte Watsford - The main antagonist of series who who enjoys the arts and sciences, but is controlling and manipulative. She causes conflict amongst the girls and steals Cleo's boyfriend Lewis. Upon transforming into a mermaid, she obtains all of the girls' collective powers, but permanently loses her abilities after a confrontation with the trio.
- Isabella "Bella" Hartley - The new girl in season three. She is a singer and performs at the juice bar. She became a mermaid in the sea caves of Ireland when she was nine, and has the power to change water into gelatine and a crystalline substance.
- Zane Bennett - who is the vain and arrogant local bad boy. In series one, he becomes obsessed with discovering the identity of the mermaids after catching a glimpse of one. He develops an on-again, off-again relationship with Rikki that is permanently broken in series three.
- Will Benjamin - A skilled swimmer and free-diver who is introduced in series three. While exploring Mako Island, he finds the moon pool and is attacked by the water, causing him to hunt for the cause of the strange event. He is Bella's love interest, and becomes closer to the girls once he discovers they are mermaids.
- Ash Dove - A keen equestrian and riding coach who appears during series two. He forms a relationship with Emma, but does not learn of her being a mermaid until the series finale.