I'm confused. Have you been taking biotin for 1 week or 2 OR are you saying that you just upped the dosage in the last week? Without knowing more info, I'd say drop down to the lowest dosage your pills allow and slowly work up OR simply sweat it out. Break outs are common for biotin, but they do go away when your body gets used to the new amount.
IMHO, it has less to do w/ water and more to do w/ your individual chemical makeup. Biotin, like other B vits, is simply flushed from the system after you body takes what it needs. However, you have may be biotin deficient (rather common nowadays) and your body is trying to adjust to its reintroduction.
When you say 2,500 and 5,000...do you mean mcgs or mgs? What's the smallest dosage of your pills?