Drought and rising sea levels have are combining to bring salty water from the ocean up the Mississippi River, making much of the region’s water undrinkable. Public health experts say the saltwater intrusion could eventually corrode the region’s aging water infrastructure, leach heavy metals into the drinking water and create other problems. Water systems engineer Treavor Boyer, a professor in the School of Sustainable Engineering and the Built Environment, part of the Fulton Schools, says that one technique being used to ease the problem — mixing fresh water with seawater — is instead creating ideal conditions for increasing levels of disinfection byproducts.