"We don't know if maybe hair clogged the drain but the tub overflowed."
He says when he first received the call from Bri's mother who was screaming that she was gone, he originally thought she meant his daughter had run away.
An autopsy was ordered to determine the cause of death.
The family of the teen, who was a junior in high school, has a GoFundMe page to raise funds for the funeral.
On the pager her father writes "My daughter Brianne Rapp passed away Friday June 1st, 2018 in her home unexpectedly at the precious age of 17."
He also says that he too, suffered an injury that caused him paralysis in a freak accident just this year.
"My daughter was the heart and soul to so many of her friends. She always put everyone else first. I, her father and Kimberly, her mother would like to put our daughter first for once to say our final goodbyes," he added.
The page is just $1,000 shy of its $9,500.
In an update to the page, her father added: "We have decided that after funeral costs are paid and bills are paid, whatever money is then remaining we are going to start a college trust fund up for her brother Tyler (12) and sister Maddy (4) in memory of Brianne."