Hi. It is natural to pass less urine in summer as much water is lost by sweat. Babies under 6 months need only breastfeeding. No need to give water unless the child has symptoms like vomiting or Diarrhea. But I understand that you had already started other foods also. If you have already started other foods, you can continue them. Small amounts(around 20 to 30 ml, 2 to 3 times ) of clean  water can be given by spoon IN BETWEEN feeds if urine is much less than normal. If water is given during feeds then baby's weight gain will come down.