The symbol also appears when water is supplied directly from the hydrant.
In order for the turntable ladder to receive water, it must be supplied by another vehicle. To do this, select the group leader of the corresponding fire engine.
When the group leader is selected, a right-click on the turntable ladder is sufficient, and a free firefighter of the vehicle builds up the water supply.
To ensure that the fire engine does not run out of water, a water supply from the hydrant is required. For this, as with the firefighting attack, simply right-click on the hydrant.