Mikvaot, Chapter Seven, Mishnah Three
Our mishnah deals with various ways in which a change in the color of the water of the mikveh can render it invalid.
1) If he rinsed in the mikveh baskets of olives or baskets of grapes and they changed its color, it remains valid.
2) Rabbi Yose says: dye-water renders it invalid by a quantity of three logs, but not merely by changing its color.
3) If wine or the sap of olives fell into it and changed its color, it becomes invalid.
4) What should one do [to make it valid again]? One should wait until the rain falls and the color reverts to the color of water.
5) If it contained forty seahs, water may be drawn and carried on the shoulder and put into it until the color reverts to that of water.
Section one: Changing the color of the water renders it invalid only if something of substance falls into the mikveh, such as grapes or olives. However, the color from the baskets that are rinsed in the mikveh does not count as a substance and therefore it does not render the mikveh invalid.
Section two: Dye water is treated like drawn water. It renders the mikveh invalid but only if there are three logs of it. A smaller amount does not render the mikveh invalid, even if it changes the color of the water
Section three: Since these do count as substances, they do render the mikveh invalid if there is enough to change the color of the water.
Section four: This section teaches how one can “fix” a mikveh that became invalid because it was colored. This mikveh does not have forty seahs of water. One can wait until the rain falls and enough water goes in so that the color returns to the normal color of water. Note that this might take a while in Israel, where rain does not fall for about half of the year (May-October).
Section five: If the mikveh already has forty seahs it is even easier to fix it if the color has changed. One can simply fill up a bucket with drawn water and add it to the mikveh, because drawn water does not invalidate a mikveh that already has forty seahs of valid water.