Drinking enough water is the best treatment for fluid retention. When the body gets less water, it perceives this as a threat to survival and begins to hold onto every drop.
Water is stored outside the cells in extracellular spaces. Signs of this can include swollen feet, legs and hands.
If you have a constant problem with fluid retention, excess salt may be the cause. The human body only tolerates salt/sodium in a certain concentration.
While the body does need salt, excess causes the body to retain fluids/water to dilute it. Drinking more water and/or reducing salt intake will allow the kidneys to flush away the excess leading to reduced fluid retention.