LOVE THIS! The Water Lock is an automatic water meter and a locking device for use on bathtub taps. What you need to do is simply set the desired volume of water for the bath and let the bathtub fill up unmonitored. You generally know how much water you would like to fill in for your bath, so after the set amount has been filled, the flow automatically stops. So you end up avoiding overspill, wastages and have the freedom to get the kids ready or do other stuff while you run the up bath water.