A blue-green sludge on your faucet is “lime scale deposits.” This limescale, also known as a scale deposit, arises from the “hard” water in your home, which contains dissolved minerals.
In its purest form, limescale appears white and can sometimes be seen in kettles and other cooking pots. However, the presence of copper pipes or fixtures might cause limescale to take on a green color.
The scale accumulation on your faucet can be removed, which will temporarily help your faucet shine again but only for a short while. To make fixtures to look their very best, you’ll need to tackle the issue where it all started: with the water coming out of your taps.