The parking for Aquaventure is by Nasimi Beach entrance (right at first Roundabout), it is free parking and there are shuttle buses that take you to the entrance.
Albeit, you could also drive to the entrance where the shuttle bus drops off (The Avenues entrance a couple of roundabouts down), and drop them off there, it is all well signposted.
I haven't been before and need to drop some guests off. However, I will need to get off as well and see them to the entrance of the park and make sure they are safely inside (and no, they are not children).