Ask your landlord to reimburse you. If they do not, hire a lawyer and do what they tell you to. The first thing they'll do is write your landlord a letter. That will probably be the end of it.

Renter's insurance? If you have it make a claim. They will likely pay, then turn around and sue either the building owner or the apartment tenant where the water came from.

Otherwise, you're probably SOL. Could try taking her to small claims court, though.

Well, from your perspective, I don't see why it matters whether the damage to you was done by your neighbor or by your neighbor's guests. It's still the neighbor's responsibility.

It does matter. Revolving-door short term tenants drastically increase the risk of incidents like this, as you'd find out immediately if you tried to insure against them. Renters are routinely required to carry some degree of insurance. If Airbnb adoption meant near-universal requirements to carry punishing insurance coverage, that's yet another externality they'd be inflicting on the market.

(I like Airbnb but see how fraught it is, too).

It does matter, but less to you and more to your insurance company.

It's more like the your renter's insurance company would sue the neighbor's company for a claim. However, since the neighbor was renting out the apartment as an Airbnb property, then their standard renter's insurance was probably invalid at the time. So now your insurance company would sue the neighbor directly and may not be able to pay.

The long term implications are that renter's insurance costs will go up for everyone in that market.

I've long thought that the biggest problem with Airbnb wasn't the tax issue, or even landlords abusing the system and running mini-hotels. It was insurance. I suspect that none of the hosts who aren't physically present (and even some who are) are violating their insurance policy, and if there is a HOA or other sort of shared space, that insurance policy would also be violated.

If hosts had to actually pay the true costs of insurance, the cost savings between traditional hotels and Airbnb would be much smaller. Now, if Airbnb actually offered the insurance to the hosts, or maintained it themselves, that would be something. But that would be fraught with fraud issues over such a wide market.

But insurance isn't a sexy topic...

The problem is that nobody can predict whether a tenant is going to abuse their lease to host short-term tenants for money. When their insurer refuses to pay up because they lied about how they use their space, there won't be any recourse through the tenant; bankrupt is bankrupt. The way around this is to require tenants to obtain expensive coverage on the presumption that they'll Airbnb the space.

In the latter case, the neighbor has a strong economic incentive to treat lawsuits by aggrieved neighbors as a cost of doing business and simply build it into the rental price charged to guests - which might be quite feasible if renting out a sufficiently desirable location.

The cost to the aggrieved neighbor of launching multiple legal actions is proportionately greater since the neighbor's recovery necessarily takes place in arrears and is not supported by a stream of guest rental income. Absent an ability to recover punitive as well as economic damages, the rentier may well find it more profitable to persist.

This leads to an interesting application of the Coase theorem, of course. If you find that your neighbor is renting out on AirBnB and you have a serious anticipation of economic loss, you are in a good position to bring your neighbor to the negotiation table and solicit compensation up front - in other words, to demand your neighbor buy you off for the predictable inconvenience. This idea will seem anathema to many entrepreneurs but it has the economic advantage of predictability, as the long-term economic cost will be the same while the transaction costs may end up being lower.

Sadly, you likely don't. AirBNB's "insurance" doesn't cover anything except the host's possessions. It doesn't cover building damage or damage to others' posessions. So, it's not true commercial insurance despite the fact that a business is being run. And transient renters statistically do a lot more damage more often than long-term (12 months or more) renters.