Both 浪费 and 糟蹋 mean "to waste." (I'm not really concerned with the other uses of 糟蹋 right now.)
I've seen the collocations 糟蹋粮食 and 糟蹋人才, and 浪费 is very common in phrases like 浪费时间 and 浪费水.
Are there situations where both 浪费 and 糟蹋 are acceptable? Are they only applied to different types of things? Is there a tonal difference between the two words? (糟蹋 seems stronger, but 浪费粮食 and 浪费人才 also sound OK to me.)