Researchers have discovered that your coffee machine could be leaching harmful elements into your coffee. In this particular study, eight coffee machines and 11 kettles were tested for the release of element ions found in coffee after it was prepared. Of the eight coffee machines the following types were tested, portafilter espresso machines, pod machines, and capsule machines.
Using standard tap water, the researchers subsequently prepared coffee in each of these types of machines for three consecutive days. Each batch of coffee was tested, and the number of element ions decreased over the course of the three days. Then, each machine was thoroughly cleaned, according to the manufacturer’s directions, in efforts of decalcifying the machine. Coffee was then subsequently prepared for another three consecutive days. Significantly higher amounts of element ions were found in the coffee that was brewed following the decalcification process.
When testing the coffee, researchers found Pb (lead), Ni (nickel), Mn (manganese), Cr (chromium), and Zn (zinc). Although elements can be naturally occurring in our environment, excessive quantities can be harmful to our health. According to this study, the amount of these elements found in the coffee prepared by a portafilter espresso machine surpassed the specific release limits allowed by the European Union. These elements reached a level that would trigger 
health concerns.
Researchers determined that portafilter espresso machines have the highest release amounts of element ions while pod and capsule machines released significantly less and in a lower concentration. The number of element ions found in coffee declined over the course of the three days before decalcification but increased following the decalcification process. Therefore, researchers advise to clean and rinse your coffee machine thoroughly, especially after a decalcification process, in the attempt to rinse away any residual element ions that could pose a health risk. No considerable amounts of elements were found in coffee brewed from the 11 kettles.
Frederic D. Müller, Christin Hackethal, Roman Schmidt, Oliver Kappenstein, Karla Pfaff & Andreas Luch (2015) Metal release from coffee machines and electric kettles, Food Additives & Contaminants: Part A, 32:11, 1959-1964, DOI: 10.1080/19440049.2015.1086929. Retrieved from https://www.tandfonline.com/doi/pdf/10.1080/19440049.2015.1086929