Water with electrolytes? I got unflavored electrolyte drops for times I fast, and for my kid who has to do band camp in the summer here. You can get flavored ones too, I don’t like them. Dilute them more than the bottle says to, sometimes a splash of lemon.

Topo Chico and orange juice is great, if you are just looking for something that tastes good.

Ask your doctor if it’s safe for you to take creatine, that certainly helps muscles retain water.