Mercury is a metal. It is available in a liquid form at room temperature. It lasts forever, when it is kept in a bottle or confined with in a thermometer, for example.
Water in an open bowl evaporates slowly in to the air. Mercury remains and does not evaporate as much. The boiling point of mercury is very high and also the heat required for liquid mercury to become gas (latent heat ) is also higher. Hence the evaporation rate is very low.
Also mercury does not react with many acids. It does not stick to other materials much, for example glass.