Is a settlement (sulh) valid regarding rainwater runoff from one rooftop onto another's roof or land?

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A settlement is valid when one agrees to allow rainwater runoff from their rooftop onto another person's roof or into their land, or from their land onto another's land. This is permissible provided the volume of flowing water is known, either through visual inspection or by area measurement, because the flow quantity varies based on the size of the roof. The location from which the water flows onto the roof must also be specified because this varies. This agreement does not require specifying a time limit, as necessity dictates this, and contracts for usufruct in cases of necessity are permissible without a fixed duration, similar to marriage contracts. The owner of the water does not acquire ownership of the watercourse itself because the usufruct of the course is not fully utilized constantly or for the majority of the time, unlike a channel (saqiyah). Furthermore, the water in a channel does not require explicit quantification because that is established by quantifying the channel itself; one cannot flow more water than the channel holds. However, surface water requires knowledge of the roof's extent because both small and large amounts of water flow from it.