Drinking water won't do anything except make you have to pee more often and be in even more pain. If it is mild then sometimes Cranberry juice can clear it up but if it really hurts that bad I would go to the doc. It's probably a UTI or bladd infection which is just a few pills of an antibiotic and you're done. I used to get them a lot when i was 16-18. Then I haven't gotten one since.