Hi. Can someone tell be at what temperature water is at it's most compact? In other words, what temperature will it start expanding by both heating, and cooling?

At 3.98 degrees C water is 0.999973 g/cc or 1.000000 g/ml, its maxium density. From there, it expands whether heated or cooled. It also expands as it freezes, ice still floats when it is in water when both have had a chance to reach 0 C.

Thanks for that Labman. Have always wondered that. Sorry about the words, "most compact". Dense is the word I was looking, and I should have known it. ;) :D