The use of pre-treatment methods for the raw water used to produce pharmaceutical grade water is growing In popularity, especially when it results In better operating reliability and a longer operating lifetime of the downstream treatment plant and equipment. Andreas Muller and Thomas Menzel, Christ AG, Switzerland, discuss the background to pretreatment, and explain when such systems are necessary and why membrane-based methods, and ultrafiltration In particular, can offer a number of advantages when it comes to the pre-treatment of raw water.