Why do we put on water weight when we eat too much?

Depends on food: Typically, if you take in too much salt, the water tends to follow the salt intake, with resultant increase in water weight. This can be stored in the body tissues. Some people are quite sensitive to salt intake regarding swelling. This can also be seen in people who when they take in too much salt, their blood pressure raises - similar reason- more fluid in the bloodstream.