ANSWER: A direct reference to dragons in the Bible can be found in at least twenty-two places in the King James' translation of the Old Testament. Some of the more fascinating references include the following.
Their wine is the poison of dragons, and the cruel venom of asps (Deuteronomy 32:33, KJV)
I am a brother to dragons, and a companion to owls (Job 30:29)
Praise the LORD from the earth, ye dragons, and all deeps: (Psalm 148:7, see also Isaiah 13:22, 27:1, 43:20, 51:9, Jeremiah 49:33, 51:34, Ezekiel 29:3, Malachi 1:3, etc.)
The vast majority of Old Testament references are derived come the word tanniym or tannim (Strong's Concordance #H8577). According to Strong's, this Hebrew word can mean a jackal, serpent, sea serpent, or even a land or sea monster. This same word was used for Moses' rod that became a snake before Egypt’s Pharaoh (Exodus 7:8 - 9).In Isaiah 34:13, 35:7 and 43:20 the original language word used is tan (Strong's #H8565), which can mean a sea serpent or other very large sea animal. Probably the closes thing that resembles the beast we imagine is in Biblical references like Psalm 74:14 where it discusses a huge beast called a Leviathan.
Let us now tackle your question about Jerusalem having a well for dragons. Nehemiah was a prophet held captive by the Persian Empire. He was released and given permission to return to Judah and rebuild Jerusalem and its walls. After arriving in the city, he toured the walls to assess their condition before reconstructing them. On his journey, he mentions something rather odd.
"And I went out by night by the gate of the valley, EVEN BEFORE THE DRAGON (Hebrew word tanniym) WELL . . ." (Nehemiah 2:13, KJV)
What do we know about this well? The New Interpreter's Commentary thinks it could be another name for the natural spring named En-rogel mentioned in 1Kings.
9. And Adonijah killed sheep and oxen and fat cattle by the Stone of Serpents, which is by En Rogel, and called all his brothers . . . (1Kings 1:9, HBFV)
The International Standard Encyclopedia thinks it was a well dug in this area. An alternative name for this particular well is jackal's well, a translation found in the New American Standard and New International Version translations. The well might have gotten its name from the wild jackals that wandered nearby, as the International Standard Encyclopedia speculates.
There is another intriguing possibility to consider. Henry Morris, in his book "The Biblical Basis for Modern Science," states that references to dragons in the Bible could actually be to dinosaurs.
"Unfortunately, because of the reluctance of modern translators to commit the Scriptures to teaching the existence of something they regard as purely mythical, modern versions commonly translate tannim by "jackals" or "serpents" or "sea monsters," depending on the context in each passage. But how can the same Hebrew word carry such a wide, even contradictory, diversity of meanings? . . .
"As a matter of fact, if one will simply translate tannim by "dinosaurs," every one of the more than 25 uses of the word becomes perfectly clear and appropriate." (The Biblical Basis for Modern Science: The Revised and Updated Classic, Chapter 12, section "Dragons and Unicorns")