This paper describes the further development of a novel laboratory technique for characterizing the scaling potential of RO feed waters. The work is focused on the CaCO3 scaling system, which is of general interest and is encountered in RO purification of Seine River water, Scaring intensity at various water recovery levels is characterized by measuring permeate flux decline and changes in pH, hardness and alkalinity of a solution recycling in the system for a certain period of time, at the tested water compositions. The objective of the present study was to test the reliability of the above intermittent recycle technique for assessing scaling propensity and anti-sealant inhibitory effectiveness by comparing speedily determined laboratory results with long duration field data, measured with Seine River water. Scale deposition thresholds in the presence of four different anti-sealants were determined in the laboratory using simulated Seine River concentrates of compositions corresponding to water recovery levers of 60-90% and of scaling potentials ranging from Langelier saturation index values (LSI) of -0.1 to 2.5. Both field and laboratory results indicated that all four tested anti-sealants enabled a water recovery level of at least 88% at LSI levels exceeding 2.0. The laboratory measurements predicted correctly the field results in three out of four cases in which a comparison was possible. This agreement lends support to the usefulness of the proposed laboratory technique for convenient characterization of scaling propensity of RO feed waters.