Numerous Massachusetts communities are spending millions of dollars on building systems capable of filtering so-called "forever chemicals" out of drinking water and more cities or towns may need to develop their own plans if the EPA implements even tighter limits. Per- and polyfluoroalkyl substances are also commonly known by the acronym PFAS. The chemicals have been around for decades in a wide variety of common products, including nonstick pans, food packaging and firefighting foam. PFAS don't degrade in the environment and have been linked to multiple health problems in humans.Their use is now mostly phased out in the U.S., but some still remain.Water systems in Massachusetts are supposed to take action if PFAS levels exceed 20 parts per trillion. As a result, many communities are building filtration facilities."It’s been extremely challenging for our public water systems to deal with PFAS," said Jennifer Pederson, of the Massachusetts Water Works Association."The goal for us is zero," the operations manager for Mansfield Water Department, Shawn Precourt, said during a recent tour of that town's new filtration facility. "To have absolutely none, and that's what this does."Mansfield's new facility costs nearly $5 million, and some communities may need multiple facilities to meet their needs. The filters also have ongoing annual costs for replacing the carbon filter medium. For Mansfield's facility, that annual cost is approximately $320,000. The cost will trickle down to ratepayers, who can expect to see an annual increase of 5% per year on their bills for the next several years in Mansfield.Concerned about the chemicals' ability to weaken children's immune systems, the EPA said last year that PFAS could cause harm at levels “much lower than previously understood.” The federal agency is considering setting the acceptable limit for PFAS in drinking water at four parts per trillion. If the EPA's proposal goes into effect, more Massachusetts communities will have to construct filtering facilities. "It's important for people to know when your water system is coming to you and asking for funding it really is because they need to invest in that system to provide you the best quality water they can," said Pederson.