Spilling water for luck
From Infogalactic: the planetary knowledge core
Spilling water for luck is a Serbian folk custom.[1][2][3] According to a Serbian belief, spilling water behind the person who goes on a journey, or to do a job, will bring good luck, and is done so that the travel or the job will end happily. It is also practiced when going to school, on an exam,[3] for a job interview, going into the army and the like.[1][3]
In ethnology, it is considered that spilled or running water symbolizes mobility and ease of movement,[2] since it does not stop or get stuck, and so spilling of water is done so that the job someone started would go as smoothly as the spilled water.[1] At the very act of spilling water in some areas it is said: "Let him go clean and clear as water."[2]