The presence of silica in brackish water greatly complicates the reverse osmosis desalting process. Threshold limits of silica scale precipitation are difficult to predict as they are influenced by a large number of parameters. Another difficulty is the lack of a silica anti-scalant that can be confidently used to extend water recovery limits. Moreover, silica scales deposited on a membrane are difficult and costly to remove. This paper describes the development of laboratory techniques for the determination of the permissible water recovery limits in desalting brackish waters containing silica and for evaluating the effectiveness of silica anti-scalants used to extend water recovery limits. Procedures enabling meaningful interpretation of silica scaling data on the basis of fundamental principles are described and illustrated by results of preliminary experiments.