Shaking water on Shabbat

Arukh Shulchan Orach Chaim, Sign 20, Section 8

The one who bathes in the river must thoroughly dry his body when he comes out of the river, so that the water will not remain on him, and he will shake off four cubits in the Carmelite basin, since when he comes out of the bath, there is a lot of water on his body, but the one who walks in public and the rain washes over his head and clothes did not take care that they are few, and even if they are many, what can he do if he is forced to do so? And this is according to the Risha ruling, it is not good for him, but for the one who bathes in the river for his own pleasure and pleasure, any light work done in this place, as he pleases, is done according to his own will.

These are exactly two explanations that I have given. And yet there is no difference in explanation. If he is clear that the prohibition is from the Lord, will we also permit it there because there is no choice? Let him stand his ground, there is no advice and no wisdom against the Lord. And taking water from the river or the river is also not acceptable to him. These explanations are extremely weak.

With regard to the explanation that they are few, it is explained in the Mishnah (11:1) that they do not have a shiur ekshava.

With regard to the explanation that ’anus is’, simply put, it is an additional level on top of an additional permission. That is, after we have determined that this is not a prohibition from the Torah (not according to the method of ekshava - ’Pam”3), we say that it is also a prohibition of the rabbis, because ‘there is no choice’, and its source is 17 there.

The source of the prohibition is on Shabbat Kama. There is extensive discussion as to whether there is anything here that is not intended, whether it is permissible here or not, and more.

In any case, I was surprised by the response, because the question of wiping after washing is a settled issue on Shabbat there, and the comparison between it and the law of walking outside during rain is brought out in the Shul explicitly (”He who bathes in a river must wipe his body thoroughly when he comes out of the river, so that the water will not remain on him and be shaken off; I am a dead man in Carmel, since when he comes out of the bath there is a lot of water on his body; but he who walks in public and the rain washes over his head and clothing, they did not observe him”), and its origin is from Torah and Rosh. Thus, regarding the questioner's question, a large amount of water is a great deal.

I didn't understand why there is no Shiur? When it rains, there is definitely a Shiur. It is no less than the water that remains on one's body when it rises from the sea. And so the city of the Tiz in the Sek there (and the Gera brought him evidence from the Toss). Hence, all the discussion of the latter who dropped it from the law of half a Shiur became unnecessary.
The source of the comparison to rain is indeed the Rosh there, and from it to the Shu'a. But the quantitative explanation does not appear in the Rosh nor does it mean in the language of the Rosh, but in the Yi. And I find the explanation difficult for me.
And in the law it is not intended and I have not seen a discussion there. Although the Ri'a in Be'er Yitzhak or in the Si'ah The fifth branch of the law makes it difficult to accept the contribution that the Psalter permitted against the prohibition of the rabbis and the law of Moses to settle.