Also find out specifically what adhesive they used. From all my research here, I don't think it's water or a "phenomenon". Have them walk you through the entire installation process, step by step, naming each product they used and what it was used for. Many installers use the same adhesive they would use for granite or other materials . . . to avoid the discoloration, you have to insist (and insist, and insist) that they use a non-bleeding adhesive. I even insisted they seal the underside where the adhesive was going to be applied (I know, probably not necessary, but the time to check everything out is beforehand - just like testing the stone before you buy to make sure it is really quartzite). I tested our White Maccabeus to make sure it was real, and made a really big deal about this potential staining situation BEFORE the installation - we actually chose our fabricators based on their answers to questions about this. If they had never heard of it, or didn't show us the kind of adhesive they would use, we moved on.
Q