# Does water boil when going through a tap (valve)?

At intermediate flow settings the pressure at the valve restriction drops nearly to zero from the Venturi effect; in water taps, this causes the water to boil momentarily at room temperature as it passes through the restriction. Bubbles of cool water vapor form and collapse at the restriction, causing the familiar hissing sound.

I don't understand why the water boils when going through the tap. Could someone explain it in more detail?

The boiling point of water is dependent from its pressure. At normal atmospheric pressure ($101325$ Pa) water boils at 100 grades Celsius, but if you reduce somehow its pressure (like it happens in a valve) its boiling temperature get lower, as you can see from this table.