Chlorinated Cyanurates: Review of Water Chemistry and Associated Drinking Water Implications

Since 1958, cyanuric acid and two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid), have been added to outdoor swimming pools to stabilize chlorine residual by minimizing sunlight related degradation. Subsequently in July 2001, dichlor and trichlor were approved for routine drinking water treatment under the United States' Federal Insecticide, Fungicide, and Rodenticide Registration Act, and manufacturers have achieved NSF 60 certification for dichlor or trichlor addition to drinking water. Currently in the United States, dichlor or trichlor drinking water use may be approved by states, tribes, or territories. One complicating factor with dichlor or trichlor is that the actual free chlorine concentration in these systems cannot be measured accurately by currently approved methods. This review summarizes the existing water chemistry associated with dichlor and trichlor use as a chlorine source in drinking water along with the associated implications.