Quite a few times now I have washed my hands, and while my hands are still wet I will touch something metal and get a static shock. I thought static electricity doesn't really build up when there's a lot of moisture, so that's why you don't get static shocks in the summer when there's more humidity. Even though it's winter now, I figured I wouldn't feel any static shocks if my hands are wet, but I still do.
Your hands may be wet, but the static charge is probably being built up by friction of your shoes against a polyester carpet or some such. Moisture on your hands is no protection against electric charge accumulatiuon.
When the air contains more moisture, electron build-up on your body and clothing is limited, as the moist air can more quickly shuttle electrons between areas of high potential and areas of low potential.
So even if you build up a large potential on your body, the constant movement of moist air relieves that potential more quickly than you can build it up without specific effort.
Moistening your hands doesn't increase the charge carrying capacity of the air around you. Further, if your clothing is carrying the charge, washing your hands may only dissipate some of it - that charge which is conducted to your body.
If the air is very dry, the charges will still generally stay where they are at, and the dissipation happens very slowly, regardless of how moist your hands are.