Abstract The experience of the authors in the design of desalination plants has developed in the two fields which feature the more industrially applicable MSF processes. Therefore the main features of the two plants at Porto Torres, both the long-tube acid-dosing type, are demonstrated. The first unit, which began operating five years ago, has a maximum capacity of 4.5 MGPD, while the second unit, the largest in the world, now in operation for three years, has a maximum capacity of 9.5 MGPD. Thereafter follow the features and the reliability and performance tests results for the plants designed and built for the Bahrain Government. These are two identical cross-tube polyphosphate dosing plants, 3 MGPD each, included in a dual purpose plant. In conformity with a request by the Government,the design and construction of the Bahrain plant was preceded by the construction of a pilot plant, built at Porto Torres. On the basis of these experiences, a synthesis of the authors conclusions about the two different design theories is presented, referring in particular to the corrosion and fouling control problems. The analysis of the two processes under comparison reveals in the authors opinion, certain elements in the acid-dosing process which make it superior to the polyphosphate dosing process.