The density of water at 25 degrees Celsius is 0.997 grams per milliliter. With the exception of temperatures from 0 to 4 degrees Celsius, the density of water decreases as the temperature rises and also decreases as the temperature falls.
As the temperature of water increases, so does its volume, forcing the constant number of particles to spread out to fill in the increased area and decrease the density. The opposite occurs as the temperature decreases. Unlike most substances, water reaches its maximum density at 4 degrees Celsius and then becomes less dense as it freezes, due to the types of bonds the molecules form.