Contaminate
Definition 1 of 3
Pro Tip 1/3
Physical Presence
Contamination often requires direct contact with the harmful substance. The sterile bandage was contaminated by dirty hands.
Pro Tip 2/3
Not Always Visible
Impurities from contamination might not be visible to the naked eye. The water looked clean, but was contaminated with bacteria.
Pro Tip 3/3
Negative Implication
'Contaminate' implies harm or degradation, not just change. The pranksters contaminated the town's fountain with dye.