Mine managed to drink half a cup of water a day plus incidental liquids in foods for gawd knows how long before I noticed. Weeks, maybe? So I wouldn't stress over a day or two.

By this point she was complaining it hurt to go to the toilet (on the rare occasions she went), had dry, wrinkly hands, cracked lips, headaches and a sore tummy. To which most of these complaints I told her to go drink some water but didn't MAKE her drink so .. she didn't. When it came to a head (after arguing until I was blue in the face that just because desert animals don't need water, doesn't mean that human girls don't) I was standing over her MAKING her drink until she got better. Grrrrrrr @ kids who don't feel thirst and can do this to themselves.