Approaching neighbour re: stormwater ingress

Howdy folks,

My partner and I have recently discovered that a significant amount of stormwater is entering the crawlspace under our house. We need to resolve this for obvious reasons, and we're currently partway through the process of getting quotes to install drainage to divert the water before it hits the crawlspace. The quotes are, unsurprisingly, expensive.

As a bit of background, we've undergone all recommended tests via our plumber to confirm that nothing is leaking on our property (drains, sewage, our stormwater system etc are all good)

From observing our block after significant rainfall, we've identified that the vast majority of the stormwater is coming from one specific corner uphill of our property. A look at Google Maps indicates that this corner sits against the block of a neighbour we've never met before, and that they have multiple structures close to our shared boundary.

In an ideal world, I'd like to understand whether there's some kind of plumbing issue at their place that is contributing to the (seemingly excessive) amount of stormwater that's flowing onto our property.

That said, I'm not sure if there's any legal requirement for our neighbours to not allow their stormwater to flow onto our block if it's going to damage our property, and if not, whether there's any way I can pitch an investigation to them in case it's a quick/easy fix.

Any and all informed advice appreciated - even if it's just "lol sounds like a you problem"!