What are trihalomethanes (THM) and haloacetic acids (HAA)?

Trihalomethanes and haloacetic acids are by-products of the disinfection process. Water is disinfected to protect against a wide variety of disease-causing organisms such as cholera, hepatitis and dysentery.  Disinfectants react with small amounts of naturally occurring matter and produce trace levels of these by-products. The California Office of Environmental Health Hazard Assessment (OEHHA) is responsible for developing Public Health Goals (PHGs) and they state, "The use of chemical disinfectants in water treatment usually results in the formation of chemical by-products. However, the risks to health from these byproducts are extremely small in comparison with the risks associated with inadequate disinfection, and it is important that the disinfection efficacy not be compromised in attempting to control such by-products.The Centers for Disease Control website provides further information on disinfection byproducts. 

Regardless, SMWD has taken several steps to reduce the levels of these by-products in the drinking water system. The vast majority of the District’s drinking water is treated with ozonation which limits the formation of these compounds. Additionally, SMWD utilizes chloramines in the distribution system which limits the formation of by-products while also preserving the microbiological quality of the water. 

1 https://oehha.ca.gov/media/downloads/crnr/haaphg013120.pdf

Show All Answers

1. What is SMWD doing to ensure that your water is safe?
2. What is a Public Health Goal (PHG)?
3. How is drinking water quality regulated?
4. What are trihalomethanes (THM) and haloacetic acids (HAA)?
5. How can I perform my own water testing?
6. Is SMWD water hard or soft?
7. What is the white residue that builds up on silverware, glasses and even my shower door?
8. Why does my tap water sometimes look cloudy?
9. Does SMWD water have PFAS in it?
10. What is the odor that I sometimes smell from my tap or sink faucet?