The water level at a certain place is the sum of the astronomical tide and the weather’s effect on the water level. Globally, semi-diurnal tides are most common, meaning two high and low tides each day.
Sea level is the average level of the ocean. Changes in sea level can be caused by many different processes that occur over different timescales. Along our coasts postglacial rebound is an important factor for determining local sea-level change.