In the Celestial Room I was looking at the octagon/ dogwood motifs on the entablature all around the room.

40 has an alphabet equivalent in Hebrew. 40 is mem. The symbol for mem is water.

(The number 40 is particularly prominent in the story of the flood. It rains for 40 days and 40 nights to cause the flood. Then after the flood Noah waits 40 days on Ararat before he sends out the raven and the dove.  40 is symbolically connected to many waters.)

Water symbolizes the throne of God: "a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb." 

I also really like the vision Ezekiel had of the waters issuing from the temple to heal the earth:

"Afterward he brought me again unto the door of the house; and, behold, waters issued out from under the threshold of the house eastward: for the forefront of the house stood toward the east, and the waters came down from under from the right side of the house, at the south side of the altar.

Then brought he me out of the way of the gate northward, and led me about the way without unto the utter gate by the way that looketh eastward; and, behold, there ran out waters on the right side.

And when the man that had the line in his hand went forth eastward, he measured a thousand cubits, and he brought me through the waters; the waters were to the ankles.

Again he measured a thousand, and brought me through the waters; the waters were to the knees. Again he measured a thousand, and brought me through; the waters were to the loins.

Afterward he measured a thousand; and it was a river that I could not pass over: for the waters were risen, waters to swim in, a river that could not be passed over.

And he said unto me, Son of man, hast thou seen this? Then he brought me, and caused me to return to the brink of the river.

Now when I had returned, behold, at the bank of the river were very many trees on the one side and on the other.

Then said he unto me, These waters issue out toward the east country, and go down into the desert, and go into the sea: which being brought forth into the sea, the waters shall be healed.

And it shall come to pass, that every thing that liveth, which moveth, whithersoever the rivers shall come, shall live: and there shall be a very great multitude of fish, because these waters shall come thither: for they shall be healed; and every thing shall live whither the river cometh."

This is also interesting:

If we look at the 40 octagons in the Celestial Room - take the 40 * 8 = 320.

In Hebrew 320 would be shin, kaf  שכ  or "shaq." The Hebrew meaning of this root word is to drink or to give to drink. If that is a coincidence, it still seems cool to me.

The symbol of water can remind us of Jesus Christ, the Living Water:

"But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life."