WICHITA, Kan. (AP) — The FBI is investigating a threat against water systems in four cities, including Wichita. FBI spokeswoman Bridget Patton confirmed on Friday that the FBI has not been able to substantiate any threats to the four cities. She would not name the other cities. Wichita spokesman Van Williams said security in the city's water system is being increased after an unspecified terrorist threat. He says the city's water is safe to drink. The Wichita Eagle reported that an internal city email it obtained Friday asked city employees to be vigilant during the next 30 days about anything hooked to a fire hydrant. Another e-mail advised plumbers in the city to call police if they see someone they don't recognize "messing with a fire hydrant or vent pipe."