From Innerpedia - Encyclopedia of Torah's Inner Dimension - Chassidut and Kabbalah
This hidden Name of God never appears explicitly in the text of the Bible, though it appears abundantly "encoded" in the form of initial letters (rashei teivot) and final letters (sofei teivot) etc, of Torah phrases. Akvah is pronounced thusly, written alef, hei, vav, hei.
It is associated in Kabbalah with the sefirah of da'at (in particular with its "right side," the concentrated power of the mind to elicit love in the heart) or, sometimes, with the sefirot of yesod (the power of the tzadik yesod olam to connect heavens and earth, as will be explained). Just as da'at is hidden within the ten sefirot from keter to malchut, so is the Name Akvah hidden throughout the Torah.
The Name Akvah is often refereed to as "the goodly Name of God," for it is numerically equal to the word "good" (tov = 17). It is the primordial light of the first day of creation which God saw to be "good" and concealed in the Torah only to be revealed to the world (the righteous souls of Israel) in the future.
It first appears in the Torah in the opening verse: "In the beginning God created the heavens and the earth." The initial letters of the four words "the heavens and the earth" spell Akvah. The preceding phrase, "God created" = 289 = 17 squared. From this we learn that God's purpose in creation is, in general, to manifest His infinite Divine goodness throughout reality, and, in particular, to combine and unite together the two created realms of "heavens" and "earth"--the spiritual realm and the physical realm.
In the Torah, "good" relates to the power of "glue" (as the prophet states: "he says to glue that it is good" [Isaiah 41:7]), the power to unite together two states of being. The Ba'al Shem Tov, whose name literally reads "The master of the goodly Name," came to the world to reveal the Divine power of this Name. In fact, each of the three words of his name are multiples of 17 (Ba'al = 102 = 6 times 17; Shem = 340 = 20 times 17; Tov = 17). He taught that the ultimate manifestation of the holy soul of Israel is its ability to be "in heaven" and "on earth" simultaneously, and thus serve as the Divine "bridge" to link and draw down the light of heaven to shine on earth. The phrase (in Yiddish) he used for this ideal state of being is "in velt ouis velt" ("in the world and out of the world," simultaneously).
Akvah, the hidden Name of God, closely resembles God's essential Name Havayah, being identical to it with the one difference that whereas the Name Havayah begins with a yud, the Name Akvah substitutes the yud with an alef (yud = 10; alef = 1, yud in mispar katan ["small numbering"]).
When each letter of Havayah (which, in particular, relates to the sefirah of wisdom) is squared the result is 186 (100 plus 25 plus 36 plus 25) which equals makom, literally "space" (the general and abstract "place" of all creation), a connotation used by the sages for God.
When the same function is applied to the Name Akvah (which, in particular, relates to the sefirah of da'at) the result is 87 (1 plus 25 plus 36 plus 25) which equals blimah, the term which the Torah uses for the "space" or "void" in which the world was created (as stated in the verse "He hangs the earth on blimah" (Job 26:7). This phrase = 913 = Breishit, "In the beginning," the first word of the Torah ).
When this same function is applied to the third four letter essential Name of God, Ekyeh (which, in particular relates to the sefirah of binah), the result is 151 (1 plus 25 plus 100 plus 25) which equals haolam, "the world."
Thus, the three Names (in their "natural" order of chochmah binah da'at ) together read "the place of the world is the [Divine] void" (mikom haolam blimah = 424 = Mashiach Ben David, who comes to the world to reveal this Divine mystery that "there is no place [even the vacuum or ?void' of creation] vacant of You").
In atbash, the Name Akvah transforms to tav, tzadik, pei, tzadik, which equals 660. 660 = "Blessed be You Havayah," the opening phrase of every blessing to God. The inner power to recognize God as the source of all blessing and to realize that source by blessing Him is the power of da'at (the power of Akvah to draw down blessing from heaven to earth).
The 4 primary "full spellings" of Akvah (which correspond to those of Havayah ), 136, 143, 154, 163, together with the corresponding "full spellings" of Havayah, 45, 52, 63, 72 = 828 (232 plus 596 = 828). The average value of each pair (828 divided by 4) = 207. 207 = or, "light" = raz, "mystery" = ein sof, "infinity" = adon olam, "the Master of the universe."