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 you taint meat with the salmonella virus, you have a disaster and a public panic.