Wanted to start introducing water after 6 months of age, but now he's …

Wanted to start introducing water after 6 months of age, but now he's only 5. It's very hot outside, the son wants to drink, and since I often go out with two children, it's not possible to give him breast milk on the street, and expressing is also quite difficult. Would you suggest giving him some water or can we come up with something else?