Drinking line isolation valves are used to turn off water to either the drinking line or the outside tap. An isolation valve is mainly used to prevent further damage if there are any leaks, however their purpose is also to stop the water going to the filter if it needs to be changed.
There are two frequently used valves; the grey valve is more common with older installations and is connected onto the copper pipework directly. This valve is typically used for outside taps as well as filters and drinking taps.
The blue/white valve is built into the plastic pipes that feed into the filter. This is usually featured in modern installations where the plastic pipe work for the filter is directly connected to the new black bypass. Typically, this valve is only used in relation to a filter and drinking line.
Both valves would need to be turned 90 degrees whenever there’s a leak or a need to change the filter.