Water draining to neighbours property

When there’s very heavy rain (this has just been an issue since El Niño) a trickle of water goes down my neighbour’s property. I thought I was fixing the issue with $3600 worth of plumbing but I’ve spoken to the plumber (we needed the plumbing fixed anyway so no big deal) and it’s actually because of the coping on our pool and he says everyone does it (that if you’re in a low lying property it pretty much always happens) so that instead of dirt going into the pool it goes into the neighbours property. He’s also said pretty much anyone a higher block has water draining into the block next to them. He said it would be very expensive to fix and not worth it. The pool has been here 40 years and it’s not a new issue.

But… I’m guessing the neighbours won’t see it that way. To me it’s such a small issue (we’re talking a trickle of water in heavy rain when everything is wet anyway) and I wouldn’t even know if it’s happening with my neighbours pool - it probably is. Anyway if they decide to force the issue would that go through council? Lawyers? I have no idea.