I occupy the ground floor apartment in a building of five floors. The drainage pipe, which is used by my four upstairs neighbors but not by me, is situated in one of my walls. Recently, the pipe started leaking into my apartment. In order to avoid damages, I promptly called in a plumber who fixed the leak preventing further damage. Since I was the one who called in the plumber I had to pay him. Since the pipe is used by my neighbors exclusively, I asked them to pay the cost of the plumber. Three of my neighbors promptly paid. However, the fourth apartment is not occupied and it is unclear even who is responsible since the owner passed away and no one has been taking care of his apartment. I told my neighbors that they have to pay the entire bill and it is their responsibility to recover their payment from the owner, but they claim that it is my responsibility to collect from the owner. Who is correct?
In order to answer your question we have to classify each of the people involved from a Torah perspective and determine who owned the problem at the outset.
It is forbidden for a person to damage another person’s property. Thus, the Gemoro (Bava Metsiyo 117) rules that if, when the upstairs neighbor washes his hands the water directly falls into the downstairs apartment, it is forbidden for the upstairs neighbor to wash his hands. The reason is that this type of direct damage is classified as girei delei–it as if the upstairs neighbor is shooting an arrow at his downstairs neighbor’s property.
Therefore, until the pipe was fixed it was forbidden for all of your upstairs neighbors to use the pipe. Thus, for example, if the water from their showers drained into the damaged pipe, none of them was allowed to take a shower until the pipe was repaired. This is an obvious deduction from the Gemara and is the ruling of contemporary poskim. (See for example page 133 of the Mishkan Shalom.) Therefore each of your upstairs neighbors had an independent problem in using the pipe.
Therefore, while the pipe was broken, each of your neighbor’s had a problem. It is not a collective problem but an individual problem for each of them to use the pipe.
There are two reasons why each of the neighbors could have forced the other three to share in the cost of repairing the pipe.
One reason is that whenever a number of individuals jointly share the same problem and when one person rectifies the problem it is rectified for all, each individual has the right to force the others to share in the cost of rectifying the problem. This principle is elucidated by the Nesivos (178, 3) and is the source for many rulings of the Gemara and Shulchan Aruch.
Thus, the Shulchan Aruch (CM 272, 15) rules that if a caravan was traveling in the desert, each traveler could force the others to share in the cost of hiring a guide and an armed escort. Similarly, the residents in a town can (CM 163) force each other to share in the cost of building a protective wall, a mikva, shul etc. The reason is that all these are joint needs. Another example brought by the Rama (264, 4) is where two people are imprisoned and it is necessary to hire someone to secure their release. The Rama goes a step further and rules that even if one of the prisoners paid in order to secure his own release from jail but intended at the same time to secure his fellow prisoner’s release, he can force his fellow prisoner to share in his costs.
Thus if you had not fixed the pipe you could have prevented all of them from using the pipe and any one of them could have forced he others to share in the cost of the repair. Had one of them repaired the pipe he could have afterwards forced the others to pay their share of the cost of the repair.
The second reason why each of them could have forced the others to share in the cost of repairing the pipe is not because of their need to use the pipe, but because the pipe is jointly owned. The Gemara (Bava Basra 42B) writes that if one partner improves the joint property all have to reimburse him for his costs.
Having established the legal classification of your four neighbors we must determine your legal classification. You had an interest in ensuring that the pipe was repaired, but you were not responsible for the pipe’s repair. When a person fixes another person’s damaged property he is improving the property and he has the legal status of a yoreid.
Having established that your four upstairs neighbors were united as partners both in the damaged pipe as well as in the problem at hand, and the fact that you were acting as a yoreid, we must determine the extent of liability that is borne by each of the partners to one who improved their joint property or rectified their joint problem. Specifically, the issue is whether each of the four partners is only liable for a quarter of the cost or is actually liable for the entire cost, but since each of the four is totally liable each can eventually collect from the other three, effectively reducing the amount each needs to pay to a quarter of the cost.
The difference between these two approaches is the point of contention between you and your neighbors. If each is liable for the entire cost, you can turn to any one of the four and force him to pay the entire cost whereas if each is only liable for a quarter, you need to collect from each of the partners.
The Rambam (Malveh Veloveh 25, 9) rules that if one partner takes a loan for the benefit of the partnership, each of the partners automatically assumes the status of a cosigner on the loan. The Rama (responsum 27, cited by the Nesivos (77, 4)) explains that the reason each assumes the status of a cosigner is because he personally, as one of the partners, benefited from the loan. The Rama (CM 77, 2) cites an opinion that if it is not known that the loan was taken for the benefit of the partnership then the other partners are not automatically liable. However, that is irrelevant in your case since what you did obviously benefited the partnership.
There is an additional dispute among the Rishonim (Rosh and Ba’al Ha’itur-see Tur siman 77) whether, in the case of a loan, one may force partner A to pay for partner B if partner B is available and able to pay for his share of the loan. However, in your situation, the fourth partner is not available and therefore, according to all opinions, you may turn to the others and force them to jointly cover your entire cost. Therefore, in your situation you can certainly collect the entire amount from the three available partners.