Given all the liquid exiting your body, you need to make sure you drink enough to compensate. Headaches are a detox symptom that may be cured with more water.
Unless you're taking Vit B's, your urine should be light staw colored -- almost clear. If it is deeper colored, you may be dehydrated.
B's cause urine to be bright yellow, so if you want to check whether you're dehydrated, stop the B's for a day.