In this paper, the effect of salts precipitators (SP) and nano-filtration (NF) on the scale deposits of multistage flash (MSF) is studied using the Skillman index for estimating the likelihood of calcium sulfate scaling. The analysis was carried out to study the sulfate scale potential for seawater with 0 to 100% pretreated make-up in an MSF reference plant. The results showed that the scale potential increases with increasing temperature and decreases with increasing the percentage of either SP or NF-treated feed. For seawater with no feed pretreatment, the scale can start depositing at 115 degrees C. However, the maximum top brine temperature (TBT), at which sulfate scale begins to precipitate, is shifted to higher temperatures with increased pretreated portion. For 100% SP-treated feed, TBT reached 170 degrees C. The temperature is shifted to 120, 135, and 145 degrees C when the NF-treated portion increases to 10, 25, and 50%, respectively. For 100% NF feed pretreatment, TBT can reach as high as 175 degrees C.