Membranes can fit in a variety of applications. They can be used post-filtration as a final polishing step; they can be used to replace existing gravity filters; and, depending on raw water quality, they can be used in lieu of an entire conventional treatment facility. The evaluation of the best membrane application for a specific water system is a balance of costs vs. risk tolerance. A number of water treatment facilities across the United States are facing facility upgrades and low-pressure membranes will undoubtedly be one of the many options considered. A number of site-specific issues must be addressed at individual facilities, and, to date, little industry guidance is available to public water systems when considering membrane technology and its most cost-effective application point. This paper highlights some of the issues that should be addressed, which are based on a real-life example recently experienced in Lancaster, Pennsylvania.