Some residents in North Bend are being warned not to drink their tap water on Wednesday after someone broke into the water tower and vandalized it Tuesday, contaminating the water supply, deputies said.

The incident is affecting the water supply of 175 homes only in the Sallal Water Association.

King County Sheriff’s Sgt. Ryan Abbott told KIRO 7 several locks were cut inside of the tower on Mt. Si Road and 480th Avenue Southeast. Power was also cut off to some parts of the tower.

The water is currently being tested.

White pellets, which investigators are calling suspicious, were left behind. The pellets, which were put into the water tank after the vandal cut out pieces of the tank to gain access, will be tested Thursday morning, Abbott said.

The FBI will join King County deputies in the investigation to determine whether the water was poisoned.