I ordered various brands from Amazon and then just took 1 tablet per 1-2 glasses of water. Initially, I simply added a bit of salt to the water. Also, I usually drink ~2x more than normally because most of the water comes from food so if you keep your usual drinking levels, you get dehydrated. I believe that's why most people feel miserable (outside initial sugar/caffeine withdrawal), because they are dehydrated and the initial 10 lbs/5 kg weight loss is all just missing water. Also, taking pure chicken broth once a week might help with getting the protein that is lost back (100-150g/week).
I think if one works from home during COVID-19, then starting on Friday, going over the worst during the weekend, and then just functioning normally during the week is a perfect way to lose weight without any measurable effects on one's work performance.
I don't water fast so I can't speak about that specifically, but I can give a good answer on oral rehydration mixtures in general. Here's the TLDR I have in a notes file on my phone:
A drink made with 6 level teaspoons of sugar and 1/2 level teaspoon of salt dissolved in 1 litre of clean water.
Be very careful to mix the correct amounts. Too much sugar can make the diarrhoea worse. Too much salt can be extremely harmful to the child.
Making the mixture a little too diluted (with more than 1 litre of clean water) is not harmful.
Ideal consumption ~30ml every few mins (or ~90mim for the 1L)
I left the child reference in as a copy/paste from... I can't remember which medical source I got it from - although my use has only been for when I or someone else wants to minimise a hangover. I once made this mix for somebody in front of a GP (doctor) who said "wow, that's exactly the 'basic rehydration recipe' we teach when we go to parts of the world where they don't have the education / equipment we have in the UK".
But that's the MVP for oral rehydration. A little potassium is good to include, and looking at the commercial tablets I have (that mix with water) they include potassium (193mg / 200ml water) and chloride (350mg / 200ml).
