Mostly the water provided by the municipality is drinking water quality in Europe. But sometimes the building and its water pipes will be so old that the pipes leak metals into the water.
No metals, this was white fluffy stuff floating in the water. And it was relatively a luxury apartment. Again this was 1977 so that's almost ancient history.
It was probably (hopefully?) just water scale from hard water building up mineral deposits on the insides of the pipes.
Common for apartments or houses that have been used for a while. Would be enough to let the water flow for a while.