Sorry for the wall of text, got a bit carried away.

Thats true but theres more then that that makes the two films similar. The main character is a loner who spends it days exploring and surviving in a apocalyptic world. Hes a man of few words that gets captured and is forced to help others to secure his own survival.The world is a polar opposite from mad max (dry wasteland vs endless ocean with no land) but the way of life for the survivirs is the same. The people are scattered around the world in a few towns (atolls) under constant threat from bandits and warlords.

Instead of cars waterworld has boats. Two very diffrent vehicles but in both movies they serve the exact same purpose: crossing the huge spaces of wasteland and fighting or evading for resources or survival. The boats also have the same worn out look as the cars in mad max and are heavily modified. The action is somewhat comparible with the first three mad max movies but obviously doesnt come to the mind blowing non stop action George Miller unleashed in Fury Road.

Altough on first glance diffrent i think waterworld must have been heavily influenced by the first three mad max movies, specially road warrior. The biggest diffrence is that Waterworld toned down the madness and cruelty of Mad Max resulting in a less daring and more family friendly movie.

Mad Max films are very unique with no other film exactly like it. Despite some diffrences in tone Waterworld is in my opinion as close as it gets.

TLDR: if you want something similar to Fury Road your out of luck because that movie has no equal yet. If you enjoy the world building, struggle to survive and the minimalist story from the Mad Max universe Waterworld might just scratch that itch.