Tea Gardens (New South Wales) – Trihalomethanes

2016/17: Tea Gardens (New South Wales): Trihalomethanes (Reticulation): 303μg/L (max), 222.5μg/L (average)

Tea Gardens water supply system achieved 99.3% of results within ADWG compared to 98.3% during 2015 – 2016. A total of 306 analytes were tested for verification monitoring in Tea Gardens reticulation system. Total trihalomethanes (THMs) were above the guideline value on two occasions. Disinfection by-products are formed when organic matter reacts with chlorine. The long detention time in reservoirs and reticulation system, partly due to low water usage outside holiday periods has contributed to these elevated readings. In response to this, water levels have been reduced in reservoirs when appropriate, and monitoring frequency has been increased.

Midcoast Water: DRINKING WATER QUALITY MANAGEMENT SYSTEM ANNUAL REPORT SUMMARY 2016-2017

2017/18: Tea Gardens (New South Wales): Trihalomethanes (Reticulation): 302μg/L (max), 246.91μg/L (average)

Tea Gardens water supply system achieved 96.0% of water quality results in the reticulation system within ADWG compared to 99.3% during 2016 – 2017. A total of 322 analytes were tested for verification monitoring in Tea Gardens reticulation system.
Results outside ADWG were total trihalomethanes (THMs) on 13 occasions.

Midcoast Water: DRINKING WATER QUALITY MANAGEMENT SYSTEM ANNUAL REPORT SUMMARY 2017-2018

Trihalomethanes Australian Guideline Level 250μg/L (0.25mg/L)

Why and how are THMs formed?
“When chlorine is added to water with organic material, such as algae, river weeds, and decaying leaves, THMs are formed. Residual chlorine molecules react with this harmless organic material to form a group of chlorinated chemical compounds, THMs. They are tasteless and odourless, but harmful and potentially toxic. The quantity of by-products formed is determined by several factors, such as the amount and type of organic material present in water, temperature, pH, chlorine dosage, contact time available for chlorine, and bromide concentration in the water. The organic matter in water mainly consists of a) humic substance, which is the organic portion of soil that remains after prolonged microbial decomposition formed by the decay of leaves, wood, and other vegetable matter; and b) fulvic acid, which is a water soluble substance of low molecular weight that is derived from humus”. US EPA