With vomiting or diarrhea, dehydration can occur. Small sips of liquid, as much as can be tolerated, are recommended during and after these bouts. With heat exhaustion to compensate for sweating and evaporation through the lungs - caused by hot weather. Prolonged exercise, or a strenuous sports event, may blunt the thirst response. You'll recognize dehydration when you have dark coloured urine with a strong odour, similar to your first urination in the morning.
Dehydration can lead to tiredness and loss of strength.
Focus on drinking enough fluids, especially if you have increased needs. Relax and enjoy decaffeinated, non-alcoholic fluids with flavour. Don't feel the need to force eight glasses of water down your esophagus every day. Personally, I prefer tasty fluids during the day and only drink water when I exercise, in hot weather, and during the night.