Weather Unit - Water versus Air

Why is it warmer in summer and milder in winter near the ocean than inland?  We did an experiment where we put a glass of water in the fridge and an empty glass in the refrigerator for 15 minutes. The empty glass was getting cold and the one with water still felt warm. The book says that air and glass lose their heat quicker than water and and water does not let the cold air in and the water keeps the glass warmer longer.  We were able to get the same results for this one.