According to Medical News Today, common causes of water retention in the legs include inactivity, obesity, inadequate protein intake, blood clots and kidney failure. Pregnant women are also prone to water retention in the legs, says Medline Plus.
Lack of exercise reduces veins' ability to transport blood from the legs to the heart, says Medical News Today. This puts pressure on the capillaries and often ruptures them, forming blood spots beneath the skin. Inactivity also weakens the lymphatic system, which regulates tissue fluid levels. Tissue fluid regulation is also affected by dietary protein. Without adequate protein, the body cannot effectively transfer fluid between the capillaries and tissues. Consequently, fluid accumulates beneath the skin.
Kidney failure is a common cause of water retention in the legs because damaged kidneys have a reduced ability to filter toxins from the bloodstream, says Medical News Today. The waste fluid remains in the body. According to WebMD, nephrotic kidney syndrome also causes water retention in the legs.
Many pregnant women experience temporary fluid retention in the legs, says WebMD. As pregnancy progresses, bodily fluid levels rise, and the growing fetus places pressure on the blood vessels that supply the legs. This type of gestational fluid retention is not dangerous, and disappears after birth. However, some pregnant women experience fluid retention caused by preeclampsia or deep vein thrombosis. Both conditions require immediate medical attention.