Taint means to contaminate. If your water supply is tainted with arsenic, you should stop drinking it right away.
Tainted and tinted are similarly spelled words with dissimilar meanings — tint is what happens when you add color to something––if you tint white with red, you get pink. On the other hand, if you taint something, you are somehow spoiling or corrupting it. If a company inadvertently taints meat with salmonella bacteria, you have a disaster and a public panic.