International Standard Bible Encyclopedia 
(גּיחון , gı̄ḥōn , גּחון , giḥōn (in 1 K), from root גּיח , gayaḥ "to burst forth"):
(1) See preceding article.
(3) A spring in Jerusalem, evidently sacred, and, for that reason, selected as the scene of Solomon's coronation ( 1 Kings 1:38 ). It is without doubt the spring known to the Moslems as ‛Ain Umm ed deraj ("the spring of the steps") and to the Christians as ‛Ain Sitti Miriam ("the spring of the lady Mary"), or commonly as the "Virgin's Fount." It is the one true spring of Jerusalem, the original source of attraction to the site of the early settlers; it is situated in the Kidron valley on the East side of "Ophel," and due South of the temple area. See Jerusalem . The water in the present day is brackish and impregnated with sewage. The spring is intermittent in character, "bursting up" at intervals: this feature may account for the name Gihon and for its sacred characters. In New Testament times it was, as it is today, credited with healing virtues. See Bethesda . Its position is clearly defined in the Old Testament. Manasseh "built an outer wall to the city of David, on the West side of Gihon, in the valley" ( = Nahal, i.e. the Kidron; 2 Chronicles 33:14 ). From Gihon Hezekiah made his aqueduct ( 2 Chronicles 32:30 ), now the Siloam tunnel. See Siloam .
The spring is approached by a steep descent down 30 steps, the water rising deep underground; the condition is due to the vast accumulation of rubbish - the result of the many destructions of the city - which now fills the valley bed. Originally the water ran down the open valley. The water rises from a long deep crack in the rock, partly under the lowest of the steps and to a lesser extent in the mouth of a small cave, 11 1/2 ft. long by 5 ft. wide, into which all the water pours. The village women of Siloam obtain the water at the mouth of the cave, but when the supply is scanty they actually go under the lowest step - where there is a kind of chamber - and fill their vessels there. At the farther end of this cave is the opening leading into the aqueduct down which the water flows to emerge after many windings at the pool of Siloam. The first part of this aqueduct is older than the time of Hezekiah and led originally to the perpendicular shaft, connected with "Warren's tunnel" described elsewhere (see Siloam; Zion ).
The preëminent position of importance which Gihon held in the eyes of the earlier inhabitants of Jerusalem is shown by the extraordinary number of passages, rock cuttings, walls and aqueducts which exist all about the spring. Walls have been made at different periods to bank up the waters and direct them into the channels provided for them. Of aqueducts, besides the "Siloam aqueduct," two others have been formed. One running from the source at a considerable lower level than that of Hezekiah was followed by the present writer (see Pefs , 1902,35-38) for 176 ft. It was very winding, following apparently the West side of the Kidron valley. It was a well-cemented channel, about 1 1/2 ft. wide and on an average of 4 1/2 ft. high, roofed in with well-cut stones. There are no certain indications of age, but in the writer's opinion it is a much later construction than Hezekiah's aqueduct, though the rock-cut part near the source may be older. It was discovered by the Siloam fellahin , because, through a fault in the dam, all the water of the "Virgin's Fount" was disappearing down this channel. A third aqueduct has recently been discovered running off at a higher level than the other two. It is a channel deeply cut in the rock with curious trough-like stones all along its floor. It appears to be made for water, but one branch of it actually slopes upward toward its end. The pottery, which is early Hebrew, shows that it is very ancient. The whole accumulated débris around the source is full of pre-Israelite and early Israelite pottery.