The vast majority of water parks have plenty of lifeguards on duty and experience zero deaths each year. Isolated accidents will happen once in a while, but water parks by and large are among the safest places to swim due to the number of staff on hand. There's no reason to increase supervision.
I won't take my kids to water parks, because there is never enough supervision to keep kids safe. The big pools especially are a problem. If they are going to let that many people in at once, there has to be more supervision. Four lifeguards can't watch hundreds of people, and kids drown because no one sees them on the bottom.
Water parks are a busy active event for children and they need more supervisions for safety such as lifeguards and security. Water park are typically crowded with rides and lots of dangers that parents may not be prepared to handle. Additional supervision would prevent injury and provide assistance. Non-swimmers may need to be given more attention as well.
Water parks need more supervision for safety. There have been numerous stories about water park attendants being injured, even killed on large slides. Water parks must do everything they can to ensure patron safety; even if it means spending more on supervision. Additional water park employees could monitor patrons better to ensure that they are properly using the park's facilities.