Yadayim, Chapter One, Mishnah Three
The next three mishnayot deal with the water used for netilat yadayim.
1) Water which had become so unfit that it could not be drunk by a beast:
a) If it was in a vessel it is invalid,
b) But if it was in the ground it is valid.
2) If there fell into [the water], dye, or gum or sulphate of copper and its color changed, it is invalid.
3) If a person did any work with it or soaked his bread in it, it is invalid.
4) Shimon of Teman says: even if he intended to soak his bread in one water and it fell into another water the water is valid.
Section one: If the water that he wants to use for netilat yadayim was so dirty that even a cow or other beast wouldn’t drink it, it can’t be used if the water has been put in a vessel. Note that this water would have to be pretty dirty, or at least it seems so to me.
But if the water is still pooled on the ground, he can use it to immerse his hands for this pool has the status of a mikveh. If he could immerse his whole body in such a pool, all the more so he can immerse his hands.
Section two: If any inks or dyes fall into the water and thereby change its color, the water can no longer be used.
Section three: Water that has used for work (perhaps as a weight on a balance) or for soaking bread, is no longer considered water and cannot be used for netilat yadayim.
Section four: Shimon of Teman (Yemen) holds that the water is disqualified for use only if he intentionally soaked his bread in it. His statement implies that it is obvious that if he didn’t intend to soak his bread in the water and the bread simply fell in, the water is still valid for use. He goes one step further. Even if he did intend to use water to soak the bread, but he intended to put the bread in one vessel and it went into another vessel, the vessel with the bread in it can still be used. The water is disqualified only if the bread goes directly into the vessel into which he intended to put it.