Depicted as a Snake with a body of Stars. Perhaps the Milky Way, which was seen as the celestial Nile. Goddess's of Purification through water. Fresh, Pure, and Sacred Water. Water is life so we could also say she is the Goddess of the Water of Life. Water refreshed the Ka while the body waited to be mummified. But we can go beyond that and point out water refresh's the body and mind, plus we need it to live. So drink lots of water, I do. Remember her attribute is that of a snake, which shows her connection to water. (because a snakes movement is fluid) This doesn't mean she's a snake. (See attribute's essay)
Manfred Lurker in The Gods and Symbols of Ancient Egypt, pretty much say's the above, but he add's that water was seen as part of the female symbolism. Water also provided Divine Grace. See page 127 of his book for more.
So we can see that Kebechet is a Goddess of Purification, yet not only does she use Water, but Incense as seen in the above text. So before a ritual or other magical /religious undertaking we would invoke Kebechet, while taking a ritual bath/shower and while cleansing the sacred space. I am some what amazed that a number of Anpu's ritual require the use of Pure water as do his offerings.
Here's a passage from the Pyramid text that deals with Kebechet:
"The Goddess Qebhut the daughter of Anpu, findeth this Pepi, and she goeth to meet him with the Four Nemset Vases. She refreshed the breast of the Great God on the day of his watch, and she refresheth the breast of this Pepi with life.
She washeth this Pepi, she censeth this Pepi."
Utterance 535 - An Wesirian Spell adapted for the King
The starry sky serves your celestial serpent, whom you love; your
orphan comes to the front, orphans are orphaned for you. You have
relieved Heru of is girdle so that he may punish the followers of
Seth. Sieze them, remove their heads, drink their blood, and claim
their hearts in this your name of Anpu Claimer of Hearts. Your eyes
have been given to you as your two urei because you are Wepwawet who
is on his standard and Anpu who presides over the Gods booth
Utterance 548 - A Resurrection Text
He goes aboard the bark like Re at the banks fo the winding waterway,
this king rows in the bark of Lightning, he navigates therein to the
Field of the Lower Skies at this south end of the Field of Rushes. His
hand is taken by Re, his head is lifted up by Atum, the end of his bow
warp is taken by Aset, his stern warp is coiled by Nebt-het, the
Celestial Serpent has placed him by Her side, she drops him down
amongst the hntwy-s as calf herds.
Utterance 582 - An ascension text
My face is that of a jackal, my middle is that of the Celestial
Serpent. I govern as Sobek who is in Shedet and as Anpu who is in Duat.
Utterance 619 - a resurrection text
Your face is that of a jackal, your middle is that of the Celestial
Serpent, your hinder parts are a broad hall a stairway has
been set up to the sky, that you may ascend and give judgement between
the two Great Gods even you whom the two Enneads support.
Utterance 674 - The king assumes royal state in the Beyond
I have found you knit together, your face is that of a jackal, your
hinder parts are the Celestial Serpent, she freshens your body in the
house of her father Anpu.
Utterance 690 - Miscellany of short utterances
O King, your sister the Celestial Serpent has cleansed you, upon the
causeway in the meadow, you having appeared to them as a jackal, as
Heru at the head of the living, as Geb at the head of the Ennead, and
as Wesir at the head of the spirits.
691B - The King as Heru calls on Wesir to wake
Quell Set as Geb, as the being who devours entrails, for your front
is that of a jackal, your hinder parts are the Celestial Serpent, your
spine is the door-bolt of the God.
1.Wilkinson, Richard H., _The Complete Gods and Goddesses of Ancient
Egypt_, Thames and Hudson, New York and London, c.2003, ISBN 0-500-