Did you ever stop to think about How Do Bathroom Taps Work. Water is a fundamental human need. Each person on Earth requires at least 20 to 50 litres of clean, safe water a day for drinking, cooking, and simply keeping themselves clean”. The principle is very simple and affective. Taps are normally constructed from solid brass for a longer life and then chrome or gold plated to add an easy to clean finish. The water pipe is connected to the bottom.  Water is then held in a chamber until required. When you want water all you need to do is turn the handle anticlockwise which unscrews an internal valve and starts the flow of  the water.
Mixers taps work on the same principle but you do need a hot and a cold water supply connected and you will get cold, warm or hot mixed water depending on where you turn the handle.
This informative plumbing video shows a cut out of a brass kitchen tap and how its designed.