Rapid dissolving effervescent tablets for treating stored water. Each tablet purifies 25 lts of water or total 225 lts of water. Tablets are foil wrapped to remain stable for 5 years or more. The formulation contains dichloroisocyanurate, an organic chlorine donor with superior disinfection capacity. Manufactured to strict specifications to ensure an accurate dose. Convenient, simple to use method of purifying stored water.