What is water weight?

what is water weight?
how do you get it / where does it come from?

'Water weight' is the apparent gain in weight you put on after losing weight by sweating off lots of perspiration. When you sweat off weight you have put you body into a dehydrated condition. You will WEIGH less, but if you maintained that dehydration level, your body would suffer greatly. When you satisfy you thirst and get your body back into a healthy balance, THAT is putting on water weight.
Do not think that the exercise was useless. While doing that exercise you burned many calories which WILL reduce your weight by a small amount. And many days of small amounts is what you are trying for.

water retention.
your body holds on the the weight you'd usually lose during sweating and toilet stuff.