I’ve done many 7 day DFs and longest 11 days. I would still need pee several times a day. Your body produces its own water and if you live in a very humid place (which I do) your pores absorbs a lot of humidity.
If you’ve only done one day before then 10 is unlikely. I managed 5 and it was hard. I don’t get the not showering or brushing your teeth. It’s unnecessary. Unless you’re a boxer trying to be in a certain weight category then don’t make your life miserable.