Mikvaos 4:5-5:1

Mikvaos 4:5

When it comes to a trough in a rock, one may not fill water in it (for preparing the ashes of the red heifer), sanctify with the ashes in it, nor sprinkle the ashes from it, nor does it require a tight-fitting lid, nor does it invalidate a mikvah. If it was a vessel and one attached it to the ground with lime, then one may fill the water in it, sanctify in it and sprinkle from it, plus it requires a tight-fitting lid and it invalidates a mikvah. If it was punctured on the bottom or on the side so that it can’t hold any water at all, it doesn’t invalidate a mikvah. Such a hole must be the width of a water skin’s spout. Rabbi Yehuda ben Baseira said that it once happened that the trough of Yehu in Jerusalem had a hole the width of a water skin’s spout and all the pure things in Jerusalem were prepared in it. Beis Shammai sent people and had it dismantled because they maintain that it retains its status as a vessel until its greater portion has been broken.

Mikvaos 5:1

If a spring is made to pass through a trough, it is unfit for immersion. If it was made to flow over the edge of the trough in any amount, what’s outside the trough is fit for immersion because a spring purifies in any volume. If it was made to pass over a pool and was then stopped, it’s like a mikvah; if it’s made to flow again, it’s unsuitable for a zav, a metzora and for preparing the purification water until we know that the original water is gone.