Eduyos chapter 7, mishnah 4. Here we have another testimony from Rabbi Tzadok, again dealing with zochalin - a small spring from which a stream of water flows out. The question discussed in the mishnah is the status of that stream when a person diverts it using the outer shell of a walnut.
The walnut's two shells:
A walnut still fresh on the tree is wrapped in a green husk, and beneath it lies the hard, brown, woody shell familiar from the walnuts sold in the market. The mishnah calls the outer husk a "leaf" of the walnut. The question is this: if someone used that husk to divert the flow of water, are the waters considered to have passed through a vessel - and once they have passed through a vessel, they are disqualified from serving as living waters.
Is a walnut husk considered a vessel?
Had a person taken a piece of wood, carved a channel into it, and used it as a sort of gutter to divert the water, the waters would certainly be disqualified, since this is a vessel in every respect. But here we are speaking of a green, fragile husk, a kind of little cup that comes off a walnut. True, it has a base and a receptacle, but it is flimsy and brittle.
The mishnah's conclusion is that this is not considered a vessel. Even though there are people who use such a husk to store small items, it lacks sufficient substance to be considered a vessel, and it is nothing more than a mere leaf. Therefore, even if the flowing spring water was diverted through it, the water remains fit for use as living waters.
The words of the mishnah:
"He'id Rabbi Tzadok al zochalin shekilchan b'aleh egoz" - spring water flowing from the spring across the ground, and a person took the green husk of a walnut and used it, half of it, to redirect the flow of the water.
"Shehen kesherin" - the water that passed through that little green cup of the walnut is valid, since the husk has no status of a vessel.
"U'mah shehayah b'Ahalya" - an incident that occurred in a place called Ahalya, where a person used such a husk to divert the water.
"U'va ma'aseh lifnei lishkas ha'gazis v'hich'shiruhu" - the question was brought before the Sanhedrin, who sat in the Chamber of Hewn Stone in Jerusalem, and they ruled the water valid to serve as living waters, like spring water, even though it had passed through that small cup-like husk.
In summary: in this mishnah Rabbi Tzadok testified that diverting flowing spring water with the outer husk of a walnut does not disqualify it, because the fragile husk has none of the substance of a vessel and is treated merely as a leaf. An incident that occurred in Ahalya was brought before the Sanhedrin in the Chamber of Hewn Stone, and they ruled the water valid.