Many basins have a small overflow hole near the top edge. It’s there to help water escape back into the drain if the tap is left running and the plug is in, or if water levels rise unexpectedly.
If that overflow hole gets clogged with soap scum, grime or debris, it can’t do its job. In a moment of distraction – a child playing with the tap, you stepping away to answer the door – water might reach the top and spill over the edge onto the floor before you notice.
Keeping the overflow clear by occasionally flushing it with water, or gently cleaning around it, gives you an extra safety margin. You still shouldn’t leave taps running unattended, of course, but if something happens, the basin has a better chance to manage the excess.
It’s a small detail that can prevent a big watery mess.
