While there are specialty valves, most have a rating stamped on them. You will see WOG on the side. This stands for Water, Oil or Gas. Most gas valves are brass and much heavier than standard valves, The other difference is most gas valves open or shut off with 1/4 turn. Ball valves also work the same way. Using a gas valve for water is more preferable than using a water valve for gas. Gas valves seal better.