Deposits on surfaces of water distribution systems can act as a sink and a source for contaminants in the water phase. An intruding contaminant will interact with the deposit and possibly be sorbed and accumulated into the more or less complex matrix of the deposit. Thus, in a contaminated system, not only the water phase is of importance but also the deposits at the inner surfaces, consisting of mineral precipitations, corrosion products, organic material and microbial biofilms. Examples for pipe wall deposits are shown in Figure 1. Contaminants accumulated in such deposits can either be released upon detachment of plaques of the deposits to the water phase or, simply, by slow migration of the contaminant from the deposit to the water (Figure 2). Therefore, deposits have to be thoroughly considered after a contamination e.g. by a deliberate attack. Deposit removal or minimization is a means for successful decontamination and the evaluation of decontamination efficacy must include the deposits.
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