Fresh water is sometimes also called potable/drinkable/clean water. However, potable/drinkable/clean water may not be fresh water always as it may be treated/cleaned water. Strictly speaking, fresh water is the natural water without any contaiminants or pollutants in it. Its composition must be 99.99 percent H2O with traces of necessary minerals/Iodine as recommended by WHO or other health experts/authorities. Our Earth is covered by seas and oceans up to 75 percent. But sea/ocean waters are not fresh. Density of pure water is maximum at 4C i.e. 1kg/L. Its density decreases up to 10 percent on freezing. For example 1L pure water may become 1.10L ice on freezing.