In every pod, mermaids who complete their training in Mermaid School are granted a Moon Ring as full initiation into the pod. Pods are governed by the Mermaid Council, which consists of elder wiser members. There are mermaid pods all around the world, which practice their own unique types of magic that differ them from one another. Although mermaids usually only have members of their own pod, mermaids from the outside are also welcome to join.
Unlike mermaids, mermen are solitary individuals. Their mothers are forced to give them up and have them be raised by land people. They have to mingle with land people, go to land school, and don't have pods due to the war that happened long ago. However, this may not be the law anymore as mermaids now trust the mermen more.
Every pod has its own set of rules, but their main concern is keeping the existence of mermaids secret from land people.
Some of the rules are the following:
- Forbidden to associate with land people and it is especially not allowed to use a Moon Ring to go on land. (That rule probably is no more because 12 mermaids on scene already have including students and Rita)
- Forbidden to let land people come onto Mako Island during a full moon, and even more so to let them into the Moon Pool.
- Forbidden to fall in love with a land person. (Rita, Sirena, and Mimmi did)
- Forbidden to travel too close to land.
- Forbidden to sing the Enchantment Song.
The pod living on the reef of Mako Island is forbidden to get legs and walk on Mako Island, especially during a full moon, although this is not really enforced.
Mermaids of their respective pods use the Full Moon as a source of magic and power. They created Moon Rings out of blue moonstones and use them to accomplish many feats, as the rings can heal or cause destruction.
Young mermaids in their respective pods must go through training to be worthy of these rings. "Mermaid School" teaches them to use their powers correctly and to be sensible in the difficult choices made through life.
Eons ago, a pod/army of mermen carried the Trident in battle and behaved in a destructive manner until mermaids from each of the 5 oceans defeated them by drawing on the powers of the oceans and locked the trident away in the Trident Cave with one of the kinder mermen's help.
The Chinese Mermaid was a member of the Eastern Pod and fell in love with a land boy. Another Eastern pod heard of this and punished the mermaid and the pod by casting a spell to turn the land boy into a Water Dragon.
Ancient mermaids used to play an ancient mermaid game and whichever mermaid got a ship to their side first won. They could use whatever powers were at their disposal.
Aurora threatened the Northern Pod and later redirected her threat to the Eastern Pod. Nerissa came to help them and fought alongside them for years. Nerissa went to face Aurora and was never seen or heard from again. During the battle, Aurora turned Nerissa into the Water Dragon and made her attack the Eastern Pod, destroying the Eastern Pod. The survivors were forced to flee to the land of China, and eventually the pod split.
A pod consisting of over a hundred mermaids took refuge on the reef of Mako Island. When Sirena, Lyla, and Nixie are charged with guarding the Moon Pool during the full moon ceremony, a boy named Zac Blakely fell into the pool by accident and became a merman. When the pod found out what happened, they blamed the girls for breaking the rule and cast them out while the rest of the pod fled to the South Pacific where they joined another pod. To correct the problem, the girls broke the rule of using a Moon Ring to go on land, and later the one that forbade singing the Enchantment Song. They then encountered Rita Santos, a mermaid of the pod who had long since found new life on land, and asked her to complete their training. In the end, Rita deemed them worthy of having Moon Rings.
With Zac Blakely being a merman, after he returns the Trident to the chamber he becomes a temporary member of the little pod formed by Sirena, Nixie, and Lyla. While Rita doesn't share their adventures, she is considered part of their pod due to her involvement with the girls in guidance and training. Sirena, Mimmi, Ondina, Evie, and Zac form a little pod in Season 2. Erik, being a merman, becomes a temporary member of the little pod formed by Mimmi, Ondina, Evie, and Zac. Weilan, being a mermaid, becomes a member of the little pod formed by Mimmi, Ondina, Evie, and Zac in Season 3.
- In H2O: Just Add Water, Cleo Sertori, Emma Gilbert, Rikki Chadwick, and Isabella Hartley can be considered a little pod. Charlotte Watsford was also a member before she turned on them. The same goes for Gracie, Julia, and Louise Chatham.
- After the events in H2O: Just Add Water and before Mako Mermaids, the H2O: Just Add Water left the Gold Coast to lead separate lives and become adults before the Pod came to live at Mako. The Moon Pool somehow changed and was made into a home by the mermaids, becoming a "sacred" place.