The Bone Snatcher (2003)

After three of its employees have been reported missing in the Southern African Namib desert, the Eland Mining exploration company mounts a search and rescue expedition, comprising more employees which team up with Dr. Zach Straker, who researches extreme survival systems. Amidst the moving sand dunes they find human bones with just some blood on it, and identify them to belong to two of the missing men; then these disappear again, and they observe a strange monster, which according to a native former herdsman is known by the local people as Esikhulu. It's able to (dis)appear, survive shotgun hits, fatally 'incorporate' human bodies -picking them off one by one- and make water turn acid...