Leaky Shutoff Valve on Water Heater

[Zzmac]

I have a leak in the cold water inlet pipe on the top of my water heater. It's coming out the threaded part of the shutoff valve right behind the blue handle (see pic). Does that whole piece with the handle just screw off where the brass bolt is?
Wouldn't be soldered on, right? Simple re & re?
Thanks everyone!

 

[Reach4]

If that is the kind of valve I am thinking of, step one would be a fractional turn (1/8?) on the bonnet nut. If that doesn't do it, maybe supplement the packing with some packing string.

But then I could be wrong about the kind of valve.