It does vary, but as long as the sources stay the same, the composition will also stay within certain limits. For instance, Munich publishes its water composition. The list combines items that you might find on a mineral water label, like calcium and magnesium, with items that you usually won't find there, like lead (don't worry, it's below 0.001 mg/l): https://www.swm.de/dam/doc/wasser/trinkwasser-analysewerte.p...