(Hillsboro, OR) -- The issue of fluoride in the public water supply is making its way back onto the ballot in Hillsboro this fall.  The local city council has approved a measure that will allow voters to tell the city water department whether they want the chemical added.  Advocates say fluoride can help prevent tooth decay and adding it to the water supply is particularly helpful for children from low-income families and marginalized groups who may not have access to adequate dental care.  Opponents say it may have unnecessary health risks.  Voters in Portland have turned down four separate water fluoridation proposals in the past, remaining the largest U.S. city without the chemical in the municipal water system.