I need gudiance. We had prayer and fasting at work, during which our boss asked for a bag of sachet water which he anointed with an oil that he said was given to him by God. He then said that whoever has an ailment of any kind should come and drink it and he will be healed. He also added that every witch or wizard in the organization will die after drinking it. Well, I refuse to drink the water, and because of this, other colleagues are acting strangely toward me, possibly thinking I'm a witch.
How should I handle this?
Your refusal was the correct thing to do. Your boss was practicing witchcraft while presenting it in the trappings of Christian terminology. He lied that God gave him the oil. He lied about what the water would do. I am positive that people were not healed after drinking the water, though some probably improved due to the placebo effect.
None of these antics are taught in the Word of God. These are merely the product of an overactive imagination.
Those who practice witchcraft pretend to have power that others do not have. They use trickery or deceit to fool people into believing their claims. See: Witchcraft. Unfortunately, you have an office full of people who accepted the lies, either because they believe the lies must be truth or because they want to make a good impression on the boss. People tend to dislike people who are different, even if they are right. "An unjust man is abominable to the righteous, and he who is upright in the way is abominable to the wicked" (Proverbs 29:27).
Fortunately, it doesn't matter what your co-workers think of you. What matters is what God thinks of you.
Be gracious to me, O God, for man has trampled upon me;
Fighting all day long he oppresses me.
My foes have trampled upon me all day long,
For they are many who fight proudly against me.
When I am afraid, I will put my trust in You.
In God, whose word I praise,
In God I have put my trust;
I shall not be afraid. What can mere man do to me?
All day long they distort my words;
All their thoughts are against me for evil.
They attack, they lurk, they watch my steps,
As they have waited to take my life.
Because of wickedness, cast them forth,
In anger put down the peoples, O God!