The Dow Chemical Co. is using new Six Sigma quality and manufacturing processes to improve its water purification technology manufacturing operation located in Minneapolis. Stricter water quality regulations and fewer sources of fresh water led to an average 15 percent annual increase in demand for FILMTEC membranes during the 1990s. Customers needed membranes shipped faster to help them meet their demand. In addition to being shipped on time, the quality of the membrane has to be high.