Chlorine Resilience Index For Water Distribution Systems

Abstract

Chlorine is one of the most used chemicals in water distribution systems because of its residual capability to protect against contamination. World health organization recommends a minimum chlorine concentration of 0.2 mg/L in the water distribution systems. However, the excessive chlorine concentration can cause unpleasant odor and taste and potentially cause cancers. Management of chlorine concentration through index is better and easier to understand. This research aimed to propose a chlorine resilience index (CRI) for water distribution systems. We applied the index to a district metering area (DMA170605) in the Samutprakarn branch. The results showed that the overall CRI value of the DMA was 0.77. The 0.77 value indicated that this DMA had chlorine mass at 77% of the appropriate level. For temporal CRI, we found that the CRI values varied between 0.67 and 0.84. The CRI values were low during 01.00-04.00 because chlorine feeding was low during the nighttime. For the case of without water loss, we found that the CRI value was 0.49, a decrease of 0.28 (36%) from the DMA with water loss. Temporal CRIs were dropped to be between 0.39 and 0.56. This implied that water loss reduction could decrease the chlorine resilience index, which may expose users to higher risks of contamination. This is due to the increasing of water ages with decreasing water loss. Therefore, whenever there are extensive water loss reduction activities in the water distribution systems, it is necessary to reconsider chlorine feeding into the system to have an appropriate chlorine concentration level.