Ventilation, shade. If they can dig into the ground in a shady spot, that will help a lot - even an inch down, the ground is much cooler than the surface, and its a big heat sink!
Water works one of two ways. First, the water from your hose, whatever, is likely cooler than the air (and is much better at thermal transfer than the air or the ground). Second, it works by evaporation, cooling things further. But warm water on hot ground just transfers heat - not its hot water, useless to the birds.
So yes, used appropriately, water can help.
Many chicken keepers in hot climates float ice in the birds waterers, offer frozen treats, and electrolyte support. and of course, choose birds well suited to the climate.
if your birds are digging into the ground under the dense shade plants, they should be fine - expect open beaks and a bit of panting, but nothing medically worrisome, I would not expect