Meltdowns at bedtime

Bedtime is depressing me lately, the meltdowns are just ridiculous. In the last say month, she’s been pushing every single boundary at bedtime. Examples, when I eventually get her out of the bath and in pjs, get her to choose 2 books, sometimes that’s hard work, but by the time the lights are off she asks for water, then for a wee, then for a poo, then for more water and more water, so she’s saves water to drink, and this is all asked each time we get back in to bed with the light off. I stay as calm as possible stating there’s no more water(after 2 times)but that’s when it turns in to a meltdown. I turn the light on, sit down, let her cry, offer cuddles, but I don’t entertain the chat about the water or I’m arguing with a 3 year old. But she then shouts ‘mummy talk to me’ and my partner thinks these meltdowns are heartbreaking, but surely I have to set a boundary? I’m there to hug and cuddle, I just don’t entertain it. What would you do in this situation? I hate that bedtimes have turned in to something so awful and she’s so worked up, and I end up very tense and pretty pissed off.