Isaiah 8 teaches that the rejection of the LORD by His people would bring about severe punishment. To illustrate this, the LORD says His people “refused the waters of Shiloah that flow gently,” and that He would bring up against them “the waters of the River” [Euphrates], that is, the Assyrians. This would not be gentle flowing, but would flood even to the neck. It would be impossible to stay afloat when that happens.
The LORD spoke to me again: “Because this people has refused the waters of Shiloah that flow gently, and rejoice over Rezin and the son of Remaliah, therefore, behold, the Lord is bringing up against them the waters of the River, mighty and many, the king of Assyria and all his glory. And it will rise over all its channels and go over all its banks, and it will sweep on into Judah, it will overflow and pass on, reaching even to the neck, and its outspread wings will fill the breadth of your land, O Immanuel.” (Isaiah 8:5-8 ESV)
From the earliest days of the city, the water source for Jerusalem was the Gihon Spring. The well-known Hezekiah’s tunnel and the new pool that he built on the west side of the city of David would not be constructed for about 25 to 35 years (2 Kings 20:20; 2 Chronicles 32:30).
The Canaanites had cut a small tunnel through the rock to allow water to flow from the Gihon Spring into the valley on the east side of what would later be called the city of David.
The comment in The IVP Bible Background Commentary: Old Testament provides a good explanation of the tunnel and pool under consideration.
Hezekiah’s tunnel had not yet been constructed at this time. Water was conducted from the Gihon Spring (in the Kidron Valley on the east side of the city) toward the south through an aqueduct that brought the water to a reservoir at the southwestern tip of the city. This aqueduct is known as the Siloam Channel and in biblical times went by the name Shiloah.
Since 1997 it has been possible for visitors to the source of the Gihon Pool to walk through the dry Canaanite tunnel and exit in the valley which is part of the Silwan village. (That exit is now within an enclosed park area known as the City of David (Jerusalem Walls) National Park.) Our photo below show a portion of that tunnel.