Oasis water purification tablets are effervescent nadcc tablets which make water safe to drink oasis water purification tablets are manufactured to an effervescent formulation containing sodium dichloroisocyanurate nadcc an organic chlorine donor with a superior disinfection capacity to sodium hypochlorite a near neutral ph and a simple easy to understand closing system for added safety hydrachem is listed by nsf international and its oasis range of water purification tablets are nsf c