Three common methods for removing soluble sulfate are reverse osmosis, distillation, or ion exchange.  Reverse Osmosis (RO) removes most dissolved substances, such as sulfate, from water by forcing the water through a semi-permeable membrane. It can typically remove between 93 and 99 percent of the sulfate.  If your sulfate is insoluble, as Calcium Sulfate, Ultrafiltration membranes can be used with much higher throughput than RO.
                                                                                  
With distillation, water is boiled and then condensed into a separate container. The dissolved substances, such as sulfate, are left behind . Distillation units can remove nearly 100 percent of sulfate. However, distillation consumes a great deal of energy and will be expensive. Ion Exchange is the most common and as the name implies, ions are exchanged, so you are trading sulfate removal for chloride addition to your water. Barium precipitation is the most effective chemical treatment method.  If chlorides are not desired, you could try Barium Nitrate that is just as effective. Barium waste is often regulated and may require special handling when it comes to disposal.  Unless you are selectively trying to remove sulfates, RO would be the best choice for soluble Sulfate.
                                                                                  
Good Luck, Greg