It takes around 1 week to lose water weight.
Here's what worked for me and I lost water weight within 7 days.
Exercise on a Regular Basis "Exercising is one of the best ways to reduce water weight".
Sleep More, Avoid Stress, Take Electrolytes, Manage your Salt Intake, Take a Magnesium Supplement,Take Dandelion Supplements and Drink plenty of Water.
Doing all the above helped me to lose water weight within a week but your results may vary.
You should at least start seeing great results within a week or two.