H2O: Tillsätt bara vatten

Cleo and Rikki face their final year of high school without Emma. They make a new friend in Bella and meet new boy Will - and encounter a strange new force on Mako Island that turns water against them.

Will seeks confirmation of his first experience on Mako Island. Bella volunteers to misdirect his search so he won't find the Moon Pool. The girls and Lewis discover the Moon Pool has changed.

Cleo seeks a new job as an assistant dolphin trainer at the Marine Park. Rikki fires Nate's band from playing at the cafe until she and Bella reach an understanding.

Cleo's forced to put Lewis' plans for romance on hold to restrain Kim's out of control love life. During this Don meets Samantha, a National Parks Manager and they start to date.

Rikki, Cleo and Lewis think they know everything there is to know about Mako Island, but when water attacks the girls in a full moon, they realise a new, potentially dangerous force is developing on the mysterious island.

Bella attempts to start a relationship with Will until she sees he's apparently got another girl. Lewis tests the magic Moon Pool water at school and attracts the attention of their Science teacher.

Rikki, Cleo and Lewis think they know everything there is to know about Mako Island, but when water attacks the girls in a full moon, they realise a new, potentially dangerous force is developing on the mysterious island.

Rikki and Bella hide out at Cleo's to protect themselves from a full moon water attack. Bella's kidnapped by a water tentacle and taken to Mako Island. Lewis tries to keep Will away from the island so the girls can rescue her.

Cleo defies Lewis' advice and experiments with the magic Moon Pool water. Using her powers, Rikki accidentally gets the water into Cleo's aquarium and all the girls have to rescue Cleo's fish Hector.

Bella's warned to back off from Will as he's on the trail of the girls' mermaid secrets. She gets too close to him and he finally discovers she's a mermaid.

Bella helps Will with his free-diving training but when she realizes he's more interested in her as a mermaid than a girl, she's hurt. Rikki and Cleo have to improvise when the cafe's first corporate function is actually a children‟s party.

Rikki receives counterfeit money at the cafe and is held captive by criminals on a boat. Bella and Cleo are forced to reveal the trio's secret to Will so they can rescue Rikki together.

Kim attempts to derail Don and Samantha's wedding. Lewis receives an opportunity to study in America. Cleo realizes she's got to let Lewis live his own life and let him go overseas.

Will pushes himself too far when Zane challenges him to prove his skills as a free-diver. The girls discover a unique crystal in the rock from the Moon Pool.

Sophie uses Bella‟s idea for a fundraising concert and presents it as her own to Rikki to gain publicity for the cafe. Cleo's caught in the crossfire with Kim when Samantha moves in and puts her stamp on the Sertori home.

Rikki's frustrated by the water attacks and goes to Mako Island on a full moon to confront the strange force in the Moon Pool. With Cleo and Bella delayed, Will pursues her and discovers she's been affected by the experience.

Cleo's introduced to Ryan, a young geophysicist who's working for Samantha. Rikki doesn't react well to Cleo consulting Ryan about the Mako rock and a fracture begins to appear in the trio.

Rikki fears Ryan's explorations on Mako Island will uncover their secrets but Cleo and Bella discount her concern. She almost goes too far trying to stop Ryan from discovering the crystals in the Moon Pool.

Will competes in the Free-Diving Championships but afterward chooses to break from the sport and shrug off Sophie's influence on his life. Rikki sees Sophie kissing Zane at the event and breaks off their relationship.

Zane installs Sophie as head of staff at the cafe. Bella develops a sneezing allergy that also accidentally triggers her powers. Sophie seizes on the problem and looks to fire Bella and the band.

The girls discover the Mako crystals contain immense energy and need to mount a rescue mission when Zane jealously steals one in an effort to gain Rikki's attention.

The girls sit their final school exams and have to avoid a water attack in public when the full moon rises early. They confront the water force in the Moon Pool and are given a message about Mako Island.

Bella's eager to ask Will to the end of year party until she sees him asking Rikki. A big misunderstanding occurs which prompts Will to express his true feelings for Bella. Sophie tries to get Zane to change the name of the cafe.

Don gets a second job at the Marine Park on the Pirate ship and outshines Cleo, threatening the future of her Dolphin show. Bella and Will find difficulty trying to connect with each others' interests.

Cleo discovers a comet is causing fish to flee the waters around Mako Island. The girls find a way to restart the message in the Moon Pool and discover the comet will collide with earth. Sophie meets Ryan and with Zane's help they join forces to remove the crystals from the Moon Pool.