In the fast growing desalination market, Hydranautics has succeeded as the technology leader, meeting the continuous challenge of providing innovative products to the desalination industry. One of the recent challenges was to develop products, which allow recovering reject water streams from varying applications. Using Hydranautics' products, water is reused by converting used "waste" water resources into high standard quality water to be used in various applications. For example, Hydranautics' membranes successfully produce high quality water from municipal wastewater. Other challenges include the successful conversion of aging plant membrane populations such as hollow fine fiber (HFF) into the latest state of art spiral wound (SW) technology for the production of high quality potable water from seawater. This paper presents two case studies of membrane conversion from HFF aramid membrane to Hydranautics' SW membrane technology. The first plant site discussed is in the Kingdom of Saudi Arabia and the second is located in Spain. Interchangeable reverse osmosis (RO) systems using SW membranes have emerged as a short/medium term objective for many RO plant owners and operators throughout the world. Conversion to SW RO technology is necessitated by the lack of availability of direct HFF membrane replacements from DuPont. In addition, the conversion from HFF membranes to SW technology helps reduce the operating costs of the plant, reduce of membrane replacements costs, and the total water cost.