A large amount of fluid is filtered by the human kidneys because the glomerular capillaries are fenestrated and are hence leakier than other capillaries.

The fenestrated nature of glomerular capillaries in the kidneys makes them highly permeable, resulting in the filtration of approximately 180 liters of fluid per day. This process, known as glomerular filtration, facilitates the removal of waste products while retaining essential substances through subsequent reabsorption in the renal tubules.