What are your night-time temperatures?
Use deep, deep shade.
Use large containers for your water, like 5 gallon buckets or larger with nipple waterers - the larger the amount of water that has to be heated up, the slower it will be heated over the course of the day, meaning the longer it will stay cool.
Insulate your buckets so they take longer to heat up during the day. Styrofoam, spray foam, Reflectix, house insulation (of course you have to make sure the chickens don't eat it because they will try). Igloo coolers (good) or double wall coolers that have a vacuum between the two walls instead of air (best). There are cup and nipple waterer adapters that will screw into an Igloo cooler
Put a large gallon block of ice into your water buckets first thing in the morning before you leave for work. It will melt throughout the day and hopefully delay the heating cycle. A frozen milk jug type gallon of water that you change out each morning could work. Like a reusable ice pack.
If all else fails, change your water every day or every other day. Bacteria as well as dehydration can kill chickens. If they're living at those hot temperatures, they're acclimated to it, the important thing is to keep the water the same temp or cooler than the chickens, not necessarily actually cold. But if the water is hotter than the chickens' body temperature, they won't drink it. Chickens run hot, around 105-107F, so as long as you keep the water lower in temp than that, they should still drink it.
If you were home during the day, I'd suggest a large block of ice you set in a casserole dish - it slowly melts, and they can drink and stand in it. But with that heat, you'd have to replace it at lunchtime at least.
