Aluminium-containing scales in water distribution systems: Prevalence and composition

Aluminium (Al) deposits in distribution systems can have important detrimental effects on tap water quality because they can increase turbidity and interfere with disinfection, and they can increase energy loss during water transport. Disruption of the scales could cause the release of associated trace metals. However, there is also the possibility that they have a protective effect on pipe surfaces and thereby reduce metal ion release, assisting with treatment optimization for regulatory compliance. However, relatively little is known about this effect and the composition of these deposits, so little reliable guidance can be given on impacts of treatment changes forced by current and anticipated regulations. In this paper, we summarize what is known about these scales and the sources of the aluminium. We also present new data on the elemental composition of scales found in selected systems in the USA and discuss implications for future study design and important areas of future research that is needed.