There are many ways to build bulging veins (improving vascularity) including losing body fat, improving your diet and using weightlifting supplements other than steroids. Genetics influence how "vascular" you appear. If genetics are not on your side, however, there are steps you can take to improve your "bulging vein" appearance. No magic supplement provides instant "bulging veins," but with hard work it can be achieved.
Consume less calories than you burn. The average male burns 2,500 calories a day while females typically burn 2,000, but if you exercise regularly you can add 300 to 500 calories to that figure. If you want to lose body fat, consume under 3,000 calories a day (male) 2,500 (female). The best way to burn calories is through regular aerobic exercise such as running, swimming or bicycling.
Drink more water. When you fail to consume enough water on a daily basis your body starts to retain the little water you do drink, so by drinking more water your telling your body it's acceptable to let go of excess water. Excess water will make you appear “puffy” and certainly less vascular.
Take kre-alkalyn and/or nitric oxide. Kre-alkalyn is a form of creatine monohydrate that delivers nutrients to your muscles via increased water retention in skeletal muscle. This serves to increase vascularity by pushing your veins to the surface of your skin via bulging, water-laden, muscles. Muscular water retention is very different from overall water retention. Nitric oxide is a commonly available weightlifting supplement essential for basic bodily functions, improves blood flow and delivers nutrients to muscles. These supplements concentrate nutrients in your blood and muscles, thus increasing the surface area of your veins, making them "bulge" out of your skin.