Usually on the back of the water heater. Look at the location outside, and then try to locate where it is inside. May have to remove a panel inside a cabinet, to gain access.
When the valve handle is "in line" with the water pipe, water will flow, calve is open. When the handle is "cross ways" with the water pipe, water will not flow, valve is off. At least this a generic description.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT