Hate to break the news I heard... Well... Apparentally there will not be a season 4 of H20 just add water, but rumors have been going around that there is a mako something show but I am not the person to go to. Hopefully you might find some more information!! Hope this helps!! Thanks. Bye bye!!
Hope this helps. There is no season 4. They r making a new show just like h2o called mako island of secrets. It is coming out in late 2012. It doesn't have the same characters. Lucy Fry from alein surf girls is playing in it. She's the only one I know of so far. Hope this answers ur questions. Thanks bye!