A water molecule in the blood enters the kidneys through the renal arteries. It is then funneled through renal vessels to the nephrons. Here the blood enters the nephrons through afferent arterioles that head towards the glomerulus. While the blood is travelling, some of its plasma enters the nephron tubules. The blood that is left leaves the glomerulus through the efferent arteriole which heads towards the peritubular capillaries and vasa recta.

Urine is created in steps. The first being filtration. In filtration, plasma is taken from the glomerulus into the glomerular capsule. The fluid that was transferred is called the glomerular filtrate and contains substances like water, nutrients and wastes.

The next step of reabsorption begins when the glomerular filtrate enters into the proximal convoluted tubule. In this step substances are pulled out of the filtrate that the body needs and are placed back into the blood. Most of the water and sodium and all of the nutrients will be removed from the filtrate. The filtrate leaves the proximal convoluted tubule and goes through the nephron loop where water and sodium continue to be pulled out of the filtrate and moved into the blood. When the filtrate has reaced the distal convoluted tubule, 95% of the sodium and 80% of the water in the filtrate has been reabsorbed.

The third and final step in urine production begins as the glomerular filtrate goes through the medulla's collecting ducts. Here, additional water can be removed from the filtrate. Whether or not this remaining water is reabsorbed depends on the body's hydration state.

With the urine now produced it leaves the kidney through the ureters and are carried to the urinary bladder. Each ureter is connected to a renal pelvis in a kidney. These are connected to major calyces which are formed by combinations of minor calyces. The urine is held in the urinary bladder until it is excreted from the body. At the base of the bladder is the urethra. This is where the water molecule is excreted from the body in the urine.