Explanation:

Statement 1: As a halogen, chlorine is a highly efficient disinfectant, and is added to public water supplies to kill disease-causing pathogens, such as bacteria, viruses, and protozoans, that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks.
Statement 2: Disinfection by chlorination can be problematic, in some circumstances. Chlorine can react with naturally occurring organic compounds found in the water supply to produce compounds known as disinfection by-products (DBPs). The most common DBPs are trihalomethanes (THMs) and haloacetic acids (HAAs).
Trihalomethanes are the main disinfectant by-products created from chlorination with two different types, bromoform and dibromochloromethane, which are mainly responsible for health hazards.
Their effects depend strictly on the duration of their exposure to the chemicals and the amount ingested into the body. In high doses, bromoform mainly slows down regular brain activity, which is manifested by symptoms such as sleepiness or sedation.