in desalination of brackish water, silica is one of the major foulants, that forms on the reverse osmosis membranes and limits the water recovery. In addition, it is a very adherent scale and once it forms, it is very difficult to clean and cleaning may damage the membrane. There are also complicating factors affecting silica fouling, such as presence of cations (e.g. Ca, Mg, etc), that usually promote silica polymerization. Pretreatment is used as a measure to reduce silica levels in the feed and hence mitigate silica fouling. This paper examines the effect of temperature, cations on silica polymerization as well as silica removal by sodium aluminate, lime and soda ash in laboratory tests using field waters.