You may be surprised to find that this study does not support the traditional sports nutrition belief that dehydration compromises performance. In the study, they found that there was a slight difference in internal temperature when dehydrated by 3%, but when comparing performance there was no difference. I will note that science shows that there can be a reduction in gastric emptying when internal heat increases, so it's best to do things to keep your body cool, such as putting ice on your core area.
Start to listen to your body and drink when your body tells you that you need fluids. Your body is your best resource.