Body weight should be back to normal before the next workout. Try hyperhydration by drinking 2-4 cups of water 30 minutes before running. Be aware of lost electrolytes if you've sweated excessively. Put an appropriate amount salt on foods and eat bananas and citrus fruit. Avoid excess protein intake.
Protein metabolism produces extra heat.
Know the signs and symptoms of heat illness and their treatments. If you have any of the symptoms, stop running, get to a cool place and consume cold fluids. If you are going to compete in an event in hot conditions, acclimatize first. Acclimatization is the process of adapting your body to be able to run more efficiently under hot environmental conditions. When it is hot the blood goes to the skin for cooling the body as well as to the working muscles.