Siman 654
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א מְקַבֶּלֶת אִשָּׁה הַלּוּלָב מִיַּד בְּנָהּ אוֹ מִיַּד בַּעֲלָהּ וּמַחְזִירָתוֹ לַמַּיִם וְתוֹסִיף עָלָיו מַיִם אִם צָרִיךְ, אֲבָל לֹא תַּחְלִיף הַמַּיִם; וּבְחֹל הַמּוֹעֵד, מִצְוָה לְהַחְלִיפָם כְּדֵי שֶׁיִּשָּׁאֵר לַח וְהָדוּר. הַגָּה: וְנוֹהֲגִין לִקַּח כָּל יוֹם חֹל הַמּוֹעֵד עֲרָבָה חֲדָשָׁה וּלְקָשְׁרָהּ בַּלּוּלָב, וְהוּא הִדּוּר מִצְוָה.
1 That one can return the lulav into water on Yom Tov: A woman can take the lulav from her son or husband, put it back in water, and add water as necessary, though she cannot switch out the water. On Hol Hamoed, it is a mitzvah to switch it out so that [the four species] stay moist and beautiful. Rema: It is the practice to take a new willow branch each day of Hol Hamoed and attach it to the lulav as a way to beautify the mitzvah.