Rashi DH b'Galgal, as well as the Gemara itself towards the end of the Amud, explains that it is prohibited to use a Galgal (pulley) to draw water from the well on Shabbos, outside of the Mikdash, in order that one should not come to draw water to irrigate his "garden or Churvah."
Why would one want to irrigate a "Churvah," a ruin?
Thank you for your attention,
Shlomo Seidenfeld, Toronto, Canada
The word "Churvah" usually brings to mind an abandoned, worthless ruin. However, we find in the Gemara (Bava Kama 57a, Bava Metzia 31a) the concept of a "Churvah ha'Mishtameres," a ruin that is enclosed by its owner in order to prevent others from trespassing. In Beitzah 8a and Sanhedrin 59b we find that it was common to spread topsoil in such a Churvah just as one does in a Ginah.
People would plant in such Churvahs small plots of garden crops, as we find in Shabbos 85a ("Arugah b' Churvah"). This is why the Gemara in Moed Katan 2a talks about irrigating one's Churvah. That is the type of Churvah that the Gemara and Rashi are referring to here.
Kollel Iyun Hadaf