Your question is unclear. But maybe this will help: When the red light is on, the 240volt current is active and may be flowing if the thermosat in the hot water heater is calling for it; when it's not on, it's there is current to the heating element in the water heater. If you have an instant-heat hot water set-up, you wasted your money on this timer -- it's for those who have hot water sitting in a tank and who want to draw current only parts of the day, say when electricity is cheaper (for those with time of day metering) or as a back-up to solar hot water on cloudy days.
I've also used this device inside a spa back when I lived in Maryland where, at that time, electricity was lots, lots cheaper at night than during the day and evening hours.
If your water heater plugs into an outlet, a regular timer will work fine. Most water heaters, however, are 220 volt lines on a dedicated circuit, thus you need something more like the WH21. Here's a good reference for you: