Question: Is rain or snow that falls on Shabbat Muktzeh and forbidden to be moved on Shabbat?
Answer: The root of this question is that there are certain foods that are forbidden for consumption on Shabbat because they were born or came into existence on Shabbat. For this reason, an egg laid by a chicken on Shabbat may not be eaten on Shabbat and is only permissible on Motza’ei Shabbat. It is likewise forbidden to move it on Shabbat (because of the prohibition of Muktzeh). Based on this, will rain or snow that has fallen on Shabbat retain the law of something which comes into existence on Shabbat and therefore be forbidden to move on Shabbat or not?
Maran Ha’Shulchan Aruch (Chapter 338) writes that if one places a bucket under a place where rain water drips, one may later move the bucket with the water inside it. If so, we see that there is no concern of Muktzeh regarding rain which falls on Shabbat. Indeed, Maran Ha’Bet Yosef (end of Chapter 310) writes explicitly in the name of the Shiboleh Ha’Leket that Rav Tzemach Gaon writes that one may wash with and drink rain water that has fallen on Shabbat or Yom Tov. Although an egg laid on Shabbat may not be moved because of its Muktzeh status as an object which has come into existence on Shabbat, this does not apply to rain water, for this water is similar to spring water which continues to flow on Shabbat and they are permitted to drink from.
The same would seemingly apply to snow which falls on Shabbat in that it does not retain a Muktzeh status and one may indeed drink it on Shabbat. It is likewise permissible to remove snow from the entrance to one’s home on Shabbat.
Nevertheless, the Responsa Lev Avraham writes that it is indeed forbidden to remove (or shovel) snow on Shabbat, for doing so includes much effort and bother and this appears like a weekday activity which is disrespectful to the Shabbat. He therefore prohibits removing snow on Shabbat. On the other hand, many Poskim disagree with his opinion and write that not every kind of hassle is forbidden on Shabbat and just as it is permissible for one to carry a heavy table on Shabbat as long as this is necessary for Shabbat, it is likewise permissible to carry, remove, and shovel snow on Shabbat using a shovel when this is necessary.
Regarding water dripping from an air conditioner on Shabbat, however, Hagaon Harav Shlomo Zalman Auerbach zt”l rules (Shulchan Shlomo page 113b) that this water retains Muktzeh status due to it being considered something which just came into existence and it is not comparable to rain which was stored in the clouds. Maran zt”l rules accordingly in his Chazon Ovadia-Shabbat, Volume 3, page 144.
Summary: Rain and snow which fall on Shabbat are not Muktzeh and they may be moved and used for drinking and washing. Nevertheless, water that drips from an air conditioner on Shabbat is Muktzeh and may not be moved.