Simply increasing the height of the water tower or increasing the pressure inside the water tower will not increase the flow of the water to the new subdivision. If a water tower already supplies the area, the only way to increase the amount of water flowing from the water tower to the subdivision is to increase the size of the pipes. The building of a new housing subdivision will result in an increased demand for water. One way to visualize how important it is for these small vessels to dilate and carry more blood to the penis at the onset of an erection is to consider an analogy of a metropolitan water system. Other risk factors associated with reduced arterial flow are a history of blunt pelvic trauma or pelvic radiation.

Such partial arterial blockage is the most common cause of organic impotence and is usually associated with risk factors such as cigarette smoking, diabetes, hypertension (high blood pressure), or even marked elevation of blood cholesterol and fat levels. Even as little as 15 percent occlusion of the small bloodvessels is enough blockage to cause a problem. As we have seen in chapter one, the small arteries carrying blood into the penis at the time of an erection must dilate from five to ten times their normal resting diameter. Problems with either the arteries carrying blood to the penis or the veins draining blood from the penis can easily prevent a satisfactory erection.