Answer:
with a towel that is damp that's what i do and it works. but not throuly with water.
First, lightly use a non-compressed air type blower to remove any larger dust or dirt particles that may be on the lens. Next use a photo grade lens cleaner such as zeiss wipes, and carefully and lightly brush in one straight direction across the lens surface. Make sure to apply very low pressure on the lens since they are "floating" within the housing and are very delicate and susceptible to damage. If you don't have the wipes, you can use 100% cotton in a pinch, but it has to be very clean. I don't recommend the very thin sheets of lens cleaning paper that are sold with cameras, since they contain wood particles and usually leave behind fibers. Never use a paper towel or clothing other than 100% cotton. Lastly use the blower lightly to dry and remove any stray dust.