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Something in the water: investigating the leaching of metals from household taps.

Abstract

Industrial activities, aging pipe infrastructure and other sources contribute to metal contamination in drinking water, an issue in many urban environments. To safeguard human health, the Ministry of Health (MoH) has maximum acceptable values for the concentrations of trace metals in drinking water supplied to New Zealand homes (DWSNZ, 2008). Contamination of water by trace metals has previously been linked to leaching from tapware and associated fittings. While the DWSNZ (2008) are unlikely to be enforceable in this context, they provide a convenient framework to determine the quality of water from these systems. This study aimed to quantify the leaching of lead (Pb), copper (Cu), zinc (Zn), nickel (Ni) and chromium (Cr) from a range of taps after a stagnation period of 1 - 14 days. Key findings • Complex chemistry occurs at the water tap interface likely involving corrosion, direct dissolution, adsorption, and precipitation, either independently or simultaneously; • Differences between taps were observed – with non-certified taps in general leaching higher concentrations of metals, though each tap behaved differently with respect to which metals were leached and when; • Generally, the biggest increase of metals in solution occurs within the first day of water stagnation, followed by a period of equilibrium; • Some of the metal concentrations from non-certified and certified taps are higher than the DWSNZ – Pb and Ni for the non-certified basin tap, Cr and Zn for the non-certified kitchen tap, Ni and Zn for the certified basin tap; • In some cases, leaching of metals can be far in excess of drinking water limits. e.g. the non-certified kitchen tap leached Zn to concentrations 7.5 times the limit after one day of stagnation; and • Some of the metal concentrations are significant relative to potential accumulation in sewage effluent or biosolids, namely Zn, which is often elevated in WWTP effluent and solids.

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