There is a water park near the University campus in Murcia. It's called Terra Natura. There is also a big theme park near Benidorm called Terra Mitica. We intend to visit both while we are out at the end of this month. Obviously, the one near Benidorm will be about a two hour drive away, but we thought we'd check it out.
If you google them you'll be able to get directions etc.
Cherrie