You can see in many pictures of lord Shiva a flow of water like this:
What exactly is it?
I would like to state that, the water which comes out of lord Shiva's hair is River Ganges or Ganga, as Bhagavata Purana depicts...
Lord Vishnu in one of his incarnations, appeared as Vamana in the sacrificial arena of Asura King Mahabali.
Then in order to measure the universe, he extended his left foot to the end of the universe and pierced a hole in its covering with the nail of his big toe. Through the hole, the pure water of the Causal Ocean (Divine Brahm-Water) entered this universe as the Ganges River.
Having washed the lotus feet of the Lord, which are covered with reddish saffron, the water of the Ganges acquired a very beautiful pink color. Because the Ganges directly touches the lotus feet of Lord Vishnu (Narayana) before descending within this universe,
Ganges is known as Bhagavat-Padi which means Emanating from the lotus feet of Bhagavan (God). It finally settles in Brahmaloka or Brahmapura, abode of Lord Brahma before descending to planet Earth at the request of Bhagiratha and held safely by Lord Shiva on his head to prevent destruction of Bhumi (Mother Earth).
Then, the river Ganges was released from Lord Shiva 's hair to meet the needs of the country according to Hindu mythology.In other legends, Himavat fathered Parvati and Ganga .
The water on Head of God Shiva is River Ganga. It is said that King Bhageeratha did Tapasya to give peace to his 60,000 ancestors who were made to ashes by an angry saint (Kapil).
Being happy with the Tapasya of Bhageeratha, God Brahma called Ganga from the sky to land on the Planet earth where the ashes of Bhageeratha ancestors were.
Since the force of River Ganga could have destroyed the Earth, God Shiva decided to land on His head. That is how God Shiva has River Ganga.
King Sagara performed a horse sacrifice (Ashwamedha yajna) to prove his supremacy. Lord Indra, the leader of the demigods, became fearful over the results of the yajna, so he decided to steal the horse. He left the horse at the ashram of Kapila, who was in deep meditation. King Sagar’s 60,000 sons, (born of Queen Sumati), and his son Asamanja (born of Queen Keshini) were then sent to find the horse. When the 60,000 sons found the horse at Kapiladeva’s ashram, they thought he had stolen it. When they prepared to attack the meditating rishi (sage), Kapila opened his eyes. Because the sons of King Sagara had disrespected such a great personality, consequently, fire emanated from their own bodies, and they were immediately burned to ashes.2
Later, King Sagara sent his grandson Amshuman to retrieve the horse. Kapiladeva returned the horse and told Anshuman that the sons of King Sagar could be delivered if the Ganges descended to earth and bathed them in her waters. King Sagar’s great-great-grandson, Bhagiratha, eventually pleased Mother Ganga, and asked her to come to earth. Mother Ganga told Bhagiratha that the force of the Ganges falling from heaven would be too great for the earth to sustain, and that she needed someone to break the fall. Bhagiratha then worshiped Lord Siva, who then agreed to accept the descending river upon his head. After the Ganga fell down on the ashes of the 60,000 sons of King Sagara they came alive and got their eternal position.
I don't think that the Bhagavata Purana actually describes the episode in which Shiva agrees to take Ganga into his hair so as to prevent her mighty flow from destroying the Earth.
This episode is, however, touched on in the Bala Kanda of the Ramayana, as part of Vishwamitra's narration to Rama. Basically, what happens is that Bhagiratha performs a penance, at the end of which he receives a boon from Brahma; he requests that the Ganga descend to Earth (1.42).
"Thousands of years have rolled by while Bhageeratha stood practising his severe ascesis, oh, dextrous Rama, and then the lord and master of all beings, namely god Brahma, is well pleased with that great-souled king's ascesis. Forefather Brahma then arrived along with assemblages of gods, and spoke this way to the great-souled Bhageeratha who is deep in the practise of ascesis.
" 'Oh, great king Bhageeratha, oh, lord of the people, I am delighted with the perfectly conducted ascesis of yours, hence oh, truly committed one, you may beseech for a boon.'
"That great resplendent and highly fortunate king Bhageeratha then remaining with suppliantly adjoined palm fold spoke to him who is the Forefather of all worlds, namely Brahma.
" 'Oh, god, if you are satisfied with my ascesis, and if there is any fruition to the ascesis of mine, let all the sons of Sagara get water oblations through me. While the ashes of these great souls are drenched with the waters of Ganga, let all of those great-grandfathers of mine depart to heaven, eternally. Oh, god, I indeed pray for offspring in our Ikshvaku dynasty, let not our dynasty dwindle as I am issueless, and oh, god, let this be the other boon to me.'
"The Forefather of all the worlds, Brahma, then replied the king who has spoken in that way, in an auspicious tongue that is sweet-sounding and sweetly worded, as well. 'Oh, top-speeded chariot-rider Bhageeratha, this aspiration of yours is sublime, and oh, the furtherer of Ikshvaku dynasty, so be it, let safeness betide you. 'This Ganga is the one with snow-broth, the elder daughter of Himavanta, and oh, king Bhageeratha, god Shiva alone is capable to sustain her force in the course of her alighting onto earth, and in fact, he is to be commissioned for that purpose.
" 'Oh, king Bhageeratha, the earth cannot endure the downfall of Ganga and to sustain Ganga, oh, king, indeed I do not behold none other than the Trident-wielder, god Shiva.' Thus Brahma spoke to Bhageeratha.
Speaking this way to the king Bhageeratha and informally greeting Ganga also, that Creator of Worlds, Brahma, left for heaven along with all the groups of gods and Wind-gods." Thus Vishvamitra continued narration about the arrival of River Ganga to earth.
The following sarga (1.43) describes the way in which Ganga descended, flowing through Shiva's hair and all of that:
"On completion of one year, he who is venerated by all worlds, the consort of Uma and the god of animals from insects to humans, that god Shiva revealed himself and spoke this to the king. Oh, best one among humans, I am delighted with your unwavering effort, and I will fulfil your cherish. I will therefore sustain Ganga, the daughter of king of mountains by my head. Afterwards, she who is reverenced by all the worlds and who is the elder daughter of Himavanta, that Ganga assuming an unendurable form and an insupportable rapidity, they say, then plunged from the sky onto the auspicious head of Shiva.
"She who is an extremely unendurable river that goddess Ganga even speculated saying to herself, 'let me enter netherworld, indeed whisking Shiva with my streams. Discerning her egotism god Shiva is infuriated, and then on his part that Three-eyed god Shiva thought to pent her up in the tufts of his head-hair. And oh, Rama, she that holy River Ganga swooped down into the cavernous curls of matted hair-tufts on the holy head of God Shiva, and she became a detainee in them. Though she strove hard in one way or another to reach the earth that Ganga is rendered incapable, as she could not gain access for an outlet from any edge of the coils of matted hair-tufts of Shiva, hence she is held there in durance vile.
"Goddess Ganga whirled round and round in the coils of tufts alone for many number of years, and when Ganga's emanation from those coils is intangible Bhageeratha again firmed up in a marvellous penance in the matter of her descent to earth. Oh, Rama, the legatee of Raghu, with that ascesis of Bhageeratha god Shiva is very much delighted, and thereupon he has also released Ganga aiming at Bindu Lake in Himalayas.
"While god Shiva released Ganga into Bindu Lake seven streams have emerged out of it, and thus three auspicious Ganga-s with holy waters have cruised eastward which are known as Hlaadini, Paavani, and Nalini. Also thus Sucakshu, Seetha, and the excellent river Sindhu are the other three rivers which streamed to the westward direction with their holy waters.
"Of them the seventh Ganga flowed towards the path of Bhageeratha' chariot, and that great-resplendent and kingly sage Bhageeratha sitting in a divine chariot moved ahead and even Ganga followed him. Thus Ganga came from heavens onto Shankara's head and from there onto the earth, and there on earth her waters advanced with a tumultuous sound advancing them.
The River Ganges is Sacred for The Hindus so much so that one is expected to take a Holy Dip in the Ganges to rid of the Sins.
Important places of Pilgrimage Centers, from Haridwar, Rudra Prayag,Gaya ,Allahabad, Benares are located on the banks of the River Ganges or its tributaries.
Lord Siva has Ganges on his Head and she is considered to be his wife.
The reference to Ganges as Lord Siva is not as frequent as, say, Lord Vishnu with SriDevi and Bhoodevi.
How come the Ganges had landed on Lord Siva’s head?
Bhagiratha a King in the Solar dynasty,ancestor of Lord Rama wanted to perform Srardha for his ancestors.
He was advised that he could not perform this as his ancestors, sons of Sagara were cursed by Sage Kapila(Founder of Nyaya System of Indian Philosophy considered an Incarnation of Lord Vishnu) and were turned into ashes.
They could be absolved of their sins and their State if Bhagiratha could somehow get the River Ganges down to Earth from the Heavens.
Ganges is believed to be at the feet of Lord Vishnu and the auspicious time if dribbles out of Vishnu’s feet is called Vishnupathi, equivalent to Pradosha of Lord Siva(read my post on Vishnupathi Punya Kaala).
On the advice of his Preceptors, Bhagiratha, started a Penance for Lord Siva.
His Penance was so powerful that Indra, fearing for his Kingdom disturbed it quite a few times,
For more on this please refer Vishnu Purana,
At one such instances the Ganges came with such a Force down to the earth, that the whole world trembled.
Bhagiratha prayed Lord Siva to control her and when Lord Siva attempted to do so, Ganges became furious, for she was from the feet of Lord Vishnu, she came down more force with the intention of drowning Lord Siva and fell on His head in torrents.
Lord Siva, angry, just let the Ganges hit Him and simply locked His braided His Locks and Ganges was stuck in His head.
This is how the Ganges landed on Sina’s head, and been so ever since.
After a lot of attempts Bhagiratha got the Ganges down to earth, had Tharpana performed.
I shall post on this later.
How come Ganges is called Lord Siva’s wife, for Siva is considered to be an Ardhanari( He is the personification of Parvati/Uma and Sivam and has shared His Sthula Body with Shakti)? Ardhanarreswara Ardhanarreswara
In fact we have a temple in Tamil nadu, Tiruchengodu where Lord Siva appears as Ardhanareeswara.
Sathi, another name for Goddess Parvathi,after her self-immolation at her father’s Home because he insulted Lord Siva, was requested by the Deavas ,Brahma and Vishnu to be reborn and be reunited with Lord Siva, for with out Her presence the Universe will not function.
She is as close to Siva as word is to meaning,
“Vagarthadaiva samprktau vagarthaa pratipattaye Jagatah pitarau vande Parvati Parameshwehvaran
” In order to achieve the comprehension of word and meaning, I salute the parents of the universe, Parvati AND Parameshwara, who are inseperable like word and its meaning.” Kumara sambhava, Kalidasa.