The series focuses on the girls dealing with everyday teen problems while trying to cope with their newfound abilities.
The first series features a single primary storyline with three main elements.
Many misinterpretations lead Cleo and Zane's loved ones to think that they are dating.
O: Just Add Water, which first aired on Network Ten in Australia and has since been broadcast in more than 120 countries worldwide.
Emma's swimming career is in jeopardy, and Cleo feels isolated when she realises that she can't go to fashionable Miriam's pool party.
Rikki soon gets fed up with their moaning, and storms off... Meanwhile, Cleo wants to tell her friend, Lewis, about her powers, but Emma and Rikki forbid it.
Series one premiered in Australia on 7 July 2006 and series two began there on 28 September 2007.
The third series premiered in the United Kingdom on 26 October 2009 while its Australian premiere occurred on .
When they enter an underground pool of water that leads to the ocean they find themselves bathed in the glow of moonlight from overhead.
After being rescued the girls return to their normal lives but soon discover they have changed: seconds after contact with water they transform into mermaids.
After further experimentation, they discover they also have unique supernatural powers over water.
During the rescue, Zane catches a glimpse of her tail and becomes obsessed with finding this "sea monster".
Doctor Denman (Lara Cox), a marine biologist, also becomes focused on the mermaids when Lewis accidentally leaves behind a genetic sample of the girls he was working on in her lab.
The girls meet Louise Chatham (Christine Amor), an older woman who reveals that she too was once a mermaid.