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Here are 12 critical facts about TTHM as the city's fight to reduce it continues: 1. Trihalomethanes are actually a group of four chemicals that are formed along with other disinfection byproducts when chlorine reacts with organic materials such as leaves or dirt in water, according to the U.S. Environmental Protection Agency. 2. TTHMs are odorless and colorless, according to the Michigan Department of Environmental Quality. That means the high levels of TTHM in Flint water last year are not related to problems such as discoloration and odor in tap water. 3. The four trihalomethane chemicals are chloroform, bromodichloromethane, dibromochloromethane and bromoform. 4. U.S. EPA regulates TTHM at a maximum allowable, annual, average level of 80 parts per billion. The standard has been in place since December 2001 for large public surface water systems and since December 2003 for small surface water and all groundwater systems. 5. Four of eight testing sites in Flint averaged more than the acceptable limit of 80 parts per billion of TTHM last year. 6. Testing for TTHM is done on a quarterly basis, which means that people who use the system are exposed to water for several months before public notice is required. That's because TTHM is a chronic -- not immediate --health threat, according to the DEQ. 7. U.S. EPA estimates the 80 parts per billion standard prevents an estimated 280 cases of bladder cancer each year out of a total of more than 330 million people who use public water supplies nationwide. 8. Since it started using the Flint River as its water source, three quarterly tests have produced these TTHM results in the city: 15 samples have been above the TTHM threshold. Nine samples have tested at less than 80 parts per billion. 9. The most recent quarterly test showed just one site of eight that was above the 80 parts per billion threshold. And a voluntary test of the same sites in late January by the city were all within were all within the limits. 10. The testin

usted iron pipes can react with residual disinfectants in drinking water distribution systems to produce carcinogenic hexavalent chromium in drinking water, reports a study by engineers at UC Riverside. Chromium is a metal that occurs naturally in the soil and groundwater.

DRIVERS-SCARCITY-INFRASTRUCTURE This study estimates the likelihood of water shortages over the remainder of the 21st century in 204 watersheds covering the contiguous United States. The estimates are based on monthly projections of water demand and renewable water supply in light of population growth and climate change, taking into account water storage and transbasin diversion capacities. The study then examines several possible adaptations to projected shortages, including water withdrawal efficiency improvements, reservoir storage enhancements, demand reductions, instream flow reductions, and groundwater depletion. Results provide a broad measure of the relative efficacy of the adaptation measures and show when and where the measures are likely to be helpful.