Scale is the precipitate that forms on surfaces in contact with water as a result of the precipitation of normally soluble solids that become insoluble as temperature increases. Some examples of scale are calcium carbonate, calcium sulphate, and calcium silicate. Scale is control by scale inhibitors.

Scale inhibitors are surface-active negatively charged polymers. As minerals exceed their solubility's and begin to merge, the polymers become attached. The structure for crystallisation is disrupted and the formation of scale is prevented. The particles of scale combined with the inhibitor will than be dispersed and remain in suspension.

Examples of scale inhibitors are phosphate esters, phosphoric acid and solutions of low molecular weight polyacrylic acid.