The tradition of throwing valuable objects into bodies of water, and in particular into natural springs and wells, is prehistoric. See this site for example - but there are many others on the subject. Archaeologists regularly excavate abandoned wells, springs, and other bodies of water in Northern Europe to uncover artifacts dating back thousands of years.

Some speculation is that the water represents an opportunity to make a transition between this and the nether worlds, so placing valuable objects into the water is a way to reach the supernatural to placate supernatural beings and to win the object of one's desire.