The production of brass traditionally requires a small amount of lead. In order to comply with food safety legislation, some manufacturers coat brass surfaces to prevent contact with water by, for example, a process called Ternary Eco Alloy (TEA). Other manufacturers switched to using so-called ‘lead-free’ brass, which contains less than 0.25% lead content. In ‘lead-free’ brass, additives such as bismuth or silicon can be used in lieu of lead to make the brass easier to machine (Choucri et al 2019).
Because ‘lead-free’ brass can contain up to 0.25% lead, some lead can be released into the water. If the water is stagnant, the amount of lead released might exceed legal guidelines for safe drinking water (Ng and Lin 2016).
Despite some scare stories about lead found in coffee from cafés, more systematic research has shown that lead exposure from coffee is fairly low (Danish EPA 2015). The lead detected in coffee seems to come from the coffee itself rather than from the equipment. According to the study,
‘Regardless of the brewing method used, all the lead present in the coffee beans was extracted [into the] brewed coffee…. There was no indication that lead was extracted from home brewing equipment.’
The researchers didn’t test espresso machines specifically, but they found that lead content in coffees from cafés in Denmark was similar to the lead content in coffees prepared in home brewers.
‘The intake of lead from coffee is low compared to the intake from other dietary sources, and it does not constitute a major part of the total dietary intake of lead.’
Other sources of lead are likely to be more impactful; the main source of lead exposure for children in the US is house dust (US CDC 2017). In fact, even your choice of coffee cup can cause lead exposure that exceeds the California Maximum Allowable Dose Level (Anderson et al 2017).