The seven liquids and the chagim
This dvar Torah is still, technically, in the works. It's meant to b"h span all of the chagim but only covers Rosh Hashanah, Sukkot and Chanukah for the moment. However, each part of the dvar Torah can be a standalone dvar Torah. Note: The basic idea of the opening and the addition at the beginning of the Chanukah section I heard in a class by Rabbi Dovid Orlofsky. My idea is to take this further and focus on each liquid and chag individually.
In Halacha there are seven liquids that are defined as "official liquids" by Halachic standards (with all sorts of ramifications), and can be remembered by the Hebrew acronym Ya"d shacha"t da"m (י"ד שח"ט ד"ם), which stands for: יין, דם, שמן, חלב, טל, דבש, מים - wine, blood, oil, milk, dew, honey and water.
Now, there's an idea that each of these liquids correlates to one of the seven Jewish holidays: Wine - Purim, Blood - Pesach (בדמיך חיי, the plague of blood), Oil - Chanukah, Milk - Shavuot, Dew - Yom Kippur (dew isn't a liquid in a regular sense and Yom Kippur isn't a holiday in a regular sense), Honey - Rosh Hashanah, Water - Sukkot (בחג נידונים על המים, we start asking for rain on Shmini Atzeret, etc).
It's obvious why honey correlates to Rosh Hashanah - wishing for a sweet new year by eating plenty of honey during the chag. What's interesting is that honey, specifically, bee's honey, is a chemical that is brought about by a non-kosher animal, which brings up the ages-old Halachic question on whether or not bee's honey is kosher (spoiler: it is).
This idea also correlates surprisingly well with the message of Yamim Noraim, The Days of Awe: Here we are finishing the year of [insert Hebrew year], for better or for worse. Some of may be feeling too much "worse". We may be feeling too impure to stand before Hashem during Rosh Hashanah and Yom Kippur. And yet, as we say before the beginning of the Yom Kippur prayers: "With the agreement of God and of the community, in the heavenly council, and in the council of man, we permit praying with transgressors." - as bad as we may feel, as far away as we may feel, Hashem is letting us once again come and stand before Him. We have another chance to purify ourselves and come back to Hashem. Like the honey which comes from an unkosher source but it itself is kosher, despite our coming out of an unkosher year, we ourselves still have our bright kernel of purity inside of us and are entering a brand new, kosher year filled with new hope.
May we all have a sweet, healthy and good new year!
Besides for "על החג נידונין על המים" and the nissuch hamayim that was in Beit Hamikdash on Sukkot, there's another connection between water and Sukkot. Of all of the liquids, water is the most klali, universal: 90% of our bodies are made up of water; 70% of the world is water - water is a central component to the well-being of the whole world. So too, Sukkot is a universal chag. Other chagim focus on more niche (but nonetheless important) things, such as commemorating various Am Yisrael-specific miraculous events (Pesach, Chanukah, Purim). But during Sukkot we would sacrifice 70 bulls for each of the 70 nations - there is an aspect of universalism here. Everyone in the world is expected to one day take part in avodat Hashem. For this, water is a central symbol of Sukkot.
Interestingly enough, the two man-made liquids correlate to the only two holidays created by our sages (man-made) and not God: Wine - Purim and Oil - Chanukah.
And we can take this idea a step further: One of the reasons that Chanukah was created was because the Jews couldn't celebrate Sukkot that year because they were busy with the war and the Temple was in the hands of the Greeks, so Chanukah was a kind of late Sukkot. But then they could've said: Well, now we have the Temple back, we don't need Chanukah and we can just celebrate the miracles of Chanukah together with Sukkot! Except, Sukkot is water and Chanukah is oil. Oil and water don't mix. Each liquid stays as it is. Each liquid, each holiday stands by itself, because each one is special in itself.