The prices for the Alton Towers annual pass to the Cariba Creek Water Park are listed online.
They aren't currently available for purchase online I think that they're available from the waterpark reception.
(We purchased ours during Feb. half term at the park, but they said that they would be available to purchase at the waterpark after half term.)
Prices are as follows:
Individual pass £65
Family 3 (Max 2 individuals 12yrs+) £156
Family 4 (Max 2 individuals 12yrs+) £208
Family 5 (Max 2 individuals 12yrs+) £260
Family 6 (Max 3 individuals 12yrs+) £312
As the price has increased, I've expired my previous post.
It seems that the original price was an introductory offer
(Sorry - I didn't know at the time otherwise I would have highlighted this!)
Not such a good deal, but as the usual entrance price is £43 for a family of 4, it still seems a good price.