Most people do retain fluid in the summer but you need some sodium try drinking a sports drink from time to time the best to you....
Why Do I Retain Water More In The Summer?
You need to drink more water. Still water and not fizzy. Your body is storing fluids due to the heat of the summer mths and so you need to drink more water...not sodas just still water. You should drink enough water that when you pee it is not a strong color yellow but very very pale yellow.