So why is snake venom in our water supply
The easiest guesses would be the plausible deniability of the toxin as you can't pin snake venom on anyone group because it's not only naturally occurring but also rapidly accentuates a naturally looking death resulting from end-organ damage. The next guess would be the deep spiritual symbolism, and connection serpents have biblically with humanity, and we all know the elite love their symbolism...
History and spirituality are intimately intertwined with serpent symbolism. Serpents originally corrupted man so the obvious symbolism would be that of a serpent tainting and corrupting man once again. During the exodus, many of these venomous snakes bit the people, and many of them died. “The wages of sin is death.” (Romans 6:23) Through the snakes, the Lord brought the Israelites to realize their sin.
Life is in the blood, and the serpent is sin. "For the life of the flesh is in the blood, and I have given you the blood to sprinkle upon the altar as an atonement for your souls; it is the blood that makes atonement because it is the life." (Lev 17:11) John, the Baptist, identified Jesus on the banks of the Jordan River. As Jesus approached John to be baptized, John said: "Behold the Lamb of God who takes away the sin of the world." (John 1:29)
Jesus is often referred to as the blood of the lamb. What I find awfully "coincidental" with this symbolism is that horses and lambs have natural antibodies to snake venom. When bitten by a snake in the wild or artificially inseminated with snake venom to produce anti-venom, the blood of the lamb or the horse immediately goes to work, producing antibodies to combat the poison.
Was the snake venom a way to filter out those of us who are spiritually protected by the blood of the lamb?
It's also worth noting that we were "given the authority to tread on serpents and scorpions, and over all the power of the enemy and nothing shall hurt you. (Luke 10:19)