EE & co-worker were re-wrapping 3787 material that's stored outside. The sacks had some water & material lying on top. When EE lifted a strap some water w/material in it dumped off top of sack onto his rt thigh. He felt the material burn his leg immediately. He flushed leg w/water immediately. When he removed his pants at end of shift he realized the burn/irritation to his thigh.