It would be trivial for WG to implement a system where, if a player drowns or destroys their own vehicle, they receive zero XP and credits for that battle. (Ideally, repeated suicides would be bannable, but let’s start small, eh?)
No need to determine intent. If it was a mistake, just pay the fine and move on. And if you’re suiciding several times per day, maybe you should rethink your gameplay.
Alternatively, since WG is not willing to enforce penalties for suiciders, perhaps there can be a “Self-Destruct” button, so you can instantly deny an enemy who’s farming you all of your HP, even if there’s no convenient body of water, cliff, or wall (to splash off of) nearby.