Hello, Thanks for trusting us with your health concern. In the current scenario, the possible causes for the post coital bleeding are an unhealthy cervix and continuation of the menstrual period perhaps due to transient hormone imbalance. Though you have been declared to be free of cervical dysplasia, the eroded cervix may still bleed on intercourse. A colposcopy may further aid in ruling out abnormal pathology and any necessary treatment can be done simultaneously. Drinking inadequate water is not the reason for the bleeding. Please report to your health care provider and get further management. Hope this helps.