"People say 'in this resource is my taniwha, my guardian spirit. He protects me, he protects my water resource. He's not your taniwha so if you are going to use that resource without my permission, he will do terrible things to you'.
I'll take the risk. Just like people who believe in taniwhas take the risk of Hell through their superstitious beliefs. But, hey, they have the freedom to believe what they want about water spirits as long as they allow the rest of us the freedom to disbelieve that those self-same water spirits can harm us.
Related link: Taniwha proof of Maori water rights